added missing examples, testimonials section, edits
added missing examples, testimonials section, edits

- minor edits
- added 'testimonials' section to showcase other libraries using clj-http

loganmhb/clj-http,nblumoe/clj-http,clyfe/clj-http,uswitch/clj-http,mtkp/clj-http,lamuria/clj-http,ducky427/clj-http,rplevy/clj-http,nathanielksmith/clj-http,matthiasn/clj-http,dakrone/clj-http