[docs] Add docs to private functions; fix typo.

The RateLimit() func is deprecated, and should not appear in the
official example.

As of [fccbb9520b (diff-e754c06a3071f63f53cee61571452b4c),) `Users.List` method was updated to `Users.ListAll`. This commit updates the documentation for `UserListOptions` to reflect that change.

API URLs starting with "/" does not play well with Github Enterprise,
whose API endpoint looks like "http(s)://hostname/api/v3/".

This fixes incorrect URLs in miletones APIs.

This change adds the fields "DiffHunk", "OriginalPosition", and "OriginalCommitId" to the PullRequestComment struct. These fields provide important information about the location of a comment.

Fixed documentation from Issue 16

Fixed GoDoc badge.

Fixes #119

Reduce variable name restriction

Updated README w/ runnable example. Addresses #32.

Fixes #66

The router now associates a regexp named group with each mux variable.
It only fills variables when capturing group name match instead of
relying on indices, which doesn't work if a variable regexp has interior
capturing groups.

Fixes #62

Add note about the availability of CurrentRoute.

This is a copy of commit d6bce32a36 from
Go core.

Issue #16: Added regex support for matching headers

Fix a typo