Change engines guide to demonstrate maintained forum
Change engines guide to demonstrate maintained forum

Change Rails engine guide to references a maintained project
Thredded instead of the abandoned project Forem. I chose
Thredded as Forem's closing note (below) suggests the choice.
https://github.com/rubysherpas/forem/blob/rails4/README.md

assain/rails,pvalena/rails,yahonda/rails,kddeisz/rails,BlakeWilliams/rails,brchristian/rails,odedniv/rails,starknx/rails,travisofthenorth/rails,odedniv/rails,esparta/rails,notapatch/rails,baerjam/rails,yhirano55/rails,mathieujobin/reduced-rails-for-travis,ngpestelos/rails,xlymian/rails,georgeclaghorn/rails,repinel/rails,marklocklear/rails,hanystudy/rails,baerjam/rails,kaspth/rails,jeremy/rails,kddeisz/rails,schuetzm/rails,flanger001/rails,lucasmazza/rails,ngpestelos/rails,vipulnsward/rails,maicher/rails,arunagw/rails,Sen-Zhang/rails,fabianoleittes/rails,maicher/rails,eileencodes/rails,Sen-Zhang/rails,yasslab/railsguides.jp,repinel/rails,printercu/rails,yahonda/rails,riseshia/railsguides.kr,palkan/rails,matrinox/rails,kenta-s/rails,bradleypriest/rails,notapatch/rails,pschambacher/rails,yalab/rails,shioyama/rails,mtsmfm/railstest,shioyama/rails,koic/rails,hanystudy/rails,kirs/rails-1,ttanimichi/rails,riseshia/railsguides.kr,kenta-s/rails,riseshia/railsguides.kr,mohitnatoo/rails,arunagw/rails,pvalena/rails,illacceptanything/illacceptanything,samphilipd/rails,iainbeeston/rails,ledestin/rails,joonyou/rails,Erol/rails,Stellenticket/rails,deraru/rails,prathamesh-sonpatki/rails,bradleypriest/rails,felipecvo/rails,illacceptanything/illacceptanything,rafaelfranca/omg-rails,mechanicles/rails,Stellenticket/rails,Spin42/rails,bradleypriest/rails,tjschuck/rails,starknx/rails,yasslab/railsguides.jp,betesh/rails,mohitnatoo/rails,tgxworld/rails,Edouard-chin/rails,jeremy/rails,rails/rails,fabianoleittes/rails,Stellenticket/rails,gcourtemanche/rails,kmayer/rails,Edouard-chin/rails,illacceptanything/illacceptanything,baerjam/rails,illacceptanything/illacceptanything,esparta/rails,gauravtiwari/rails,georgeclaghorn/rails,assain/rails,samphilipd/rails,alecspopa/rails,assain/rails,vipulnsward/rails,BlakeWilliams/rails,kirs/rails-1,fabianoleittes/rails,EmmaB/rails-1,kmcphillips/rails,travisofthenorth/rails,MSP-Greg/rails,Edouard-chin/rails,lcreid/rails,jeremy/rails,Erol/rails,mechanicles/rails,mijoharas/rails,yalab/rails,schuetzm/rails,Spin42/rails,pschambacher/rails,tgxworld/rails,yhirano55/rails,Stellenticket/rails,palkan/rails,travisofthenorth/rails,matrinox/rails,yhirano55/rails,alecspopa/rails,tgxworld/rails,gcourtemanche/rails,kmcphillips/rails,Spin42/rails,bogdanvlviv/rails,vipulnsward/rails,odedniv/rails,gauravtiwari/rails,untidy-hair/rails,gcourtemanche/rails,untidy-hair/rails,Erol/rails,kaspth/rails,rails/rails,brchristian/rails,untidy-hair/rails,repinel/rails,yahonda/rails,prathamesh-sonpatki/rails,illacceptanything/illacceptanything,printercu/rails,illacceptanything/illacceptanything,MSP-Greg/rails,ledestin/rails,alecspopa/rails,gfvcastro/rails,betesh/rails,hanystudy/rails,tjschuck/rails,illacceptanything/illacceptanything,utilum/rails,aditya-kapoor/rails,shioyama/rails,notapatch/rails,illacceptanything/illacceptanything,deraru/rails,illacceptanything/illacceptanything,kmcphillips/rails,yawboakye/rails,Vasfed/rails,tgxworld/rails,eileencodes/rails,kmayer/rails,joonyou/rails,rails/rails,MSP-Greg/rails,vipulnsward/rails,ngpestelos/rails,travisofthenorth/rails,riseshia/railsguides.kr,Envek/rails,illacceptanything/illacceptanything,eileencodes/rails,deraru/rails,koic/rails,marklocklear/rails,arunagw/rails,Sen-Zhang/rails,tjschuck/rails,iainbeeston/rails,kamipo/rails,illacceptanything/illacceptanything,repinel/rails,koic/rails,pvalena/rails,kirs/rails-1,bogdanvlviv/rails,gfvcastro/rails,BlakeWilliams/rails,Vasfed/rails,georgeclaghorn/rails,gauravtiwari/rails,mtsmfm/railstest,bolek/rails,bogdanvlviv/rails,georgeclaghorn/rails,bolek/rails,flanger001/rails,pvalena/rails,bogdanvlviv/rails,palkan/rails,EmmaB/rails-1,betesh/rails,mathieujobin/reduced-rails-for-travis,tjschuck/rails,kmayer/rails,arunagw/rails,kmcphillips/rails,rafaelfranca/omg-rails,kaspth/rails,kamipo/rails,aditya-kapoor/rails,yawboakye/rails,mohitnatoo/rails,Envek/rails,yhirano55/rails,yahonda/rails,gfvcastro/rails,mtsmfm/railstest,kamipo/rails,mijoharas/rails,pschambacher/rails,iainbeeston/rails,illacceptanything/illacceptanything,assain/rails,bolek/rails,Vasfed/rails,gfvcastro/rails,utilum/rails,lcreid/rails,rossta/rails,mechanicles/rails,notapatch/rails,kddeisz/rails,ttanimichi/rails,EmmaB/rails-1,untidy-hair/rails,rossta/rails,rossta/rails,deraru/rails,mathieujobin/reduced-rails-for-travis,joonyou/rails,printercu/rails,betesh/rails,flanger001/rails,joonyou/rails,fabianoleittes/rails,mijoharas/rails,esparta/rails,Erol/rails,kddeisz/rails,xlymian/rails,Envek/rails,kenta-s/rails,shioyama/rails,BlakeWilliams/rails,felipecvo/rails,brchristian/rails,ledestin/rails,lucasmazza/rails,illacceptanything/illacceptanything,rafaelfranca/omg-rails,yalab/rails,schuetzm/rails,schuetzm/rails,felipecvo/rails,palkan/rails,eileencodes/rails,jeremy/rails,printercu/rails,yalab/rails,samphilipd/rails,rails/rails,starknx/rails,baerjam/rails,lcreid/rails,prathamesh-sonpatki/rails,marklocklear/rails,esparta/rails,utilum/rails,utilum/rails,yawboakye/rails,maicher/rails,iainbeeston/rails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