Remove dead links and add working links
Remove dead links and add working links

Changes:
==========
1. Added working link to rlwrap
2. Fix the outdated twitter link
3.  make folders look like folder  e.g t/spec to `t/spec`
4. make command line flags appear clear in markdown
5. Fix link to the p6lert commandline script
6. make markdown easy to read, add some formatting
tony-o/rakudo,nbrown/rakudo,softmoth/rakudo,tony-o/rakudo,labster/rakudo,salortiz/rakudo,tony-o/rakudo,salortiz/rakudo,nbrown/rakudo,softmoth/rakudo,rakudo/rakudo,nbrown/rakudo,tbrowder/rakudo,tony-o/rakudo,salortiz/rakudo,labster/rakudo,MasterDuke17/rakudo,tony-o/rakudo,salortiz/rakudo,nbrown/rakudo,rakudo/rakudo,softmoth/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,rakudo/rakudo,tbrowder/rakudo,tbrowder/rakudo,tbrowder/rakudo,rakudo/rakudo,salortiz/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,nbrown/rakudo,labster/rakudo,tbrowder/rakudo,nbrown/rakudo,tony-o/rakudo,softmoth/rakudo,MasterDuke17/rakudo,labster/rakudo,salortiz/rakudo,rakudo/rakudo,labster/rakudo,rakudo/rakudo,softmoth/rakudo,MasterDuke17/rakudo,labster/rakudo