Add links to RCurl and curl

You have links to the other libraries, so might as well link to these as well.
Merge pull request #123 from jimhester/patch-1

Add links to RCurl and curl
Change a partial match to a full match
Notes for release
Merge branch 'master' of github.com:hadley/httr
Version bump
Specify both handle & url
Make headers generic
code correction
Merge pull request #125 from cwickham/patch-1

code correction
Fixed cookie variable format issue

Ref:
http://stackoverflow.com/questions/25374231/copying-cookie-for-httr/2538
1506#25381506
Merge pull request #132 from hrbrmstr/master

Fixed cookie variable format issue
Fix url_ok bug, status codes are integers
Merge pull request #133 from gaborcsardi/master

Fix url_ok bug, status codes are integers
Merge pull request #124 from scottkosty/patch-1

Change a partial match to a full match
Add news entry for url_ok() fix (#133)
Merge pull request #134 from gaborcsardi/master

Add news entry for url_ok() fix (#133)
clarify required GitHub application information

Make it clear that the application URL can be anything, and that
the required credentials are the client ID and secret. Closes #131.
Merge pull request #135 from garfieldnate/patch-1

clarify required GitHub application information
Use readBin instead of rawToChar