Added docs for merge

I was about to submit a feature request for merge, but found it was already there, just not documented.  Here's the missing documentation.
Merge pull request #77 from aearly/patch-1

Added docs for merge
Remove docs about using strings as functions
Fixes minor typo
Merge pull request #83 from lfac-pt/patch-1

Fixes minor typo
Merge pull request #80 from aearly/patch-1

Remove docs about using strings as functions
Fixes small typos
Merge pull request #84 from zertosh/fix-typos

Fixes small typos