Implements multiple selections clipboard paste

Includes:

  - Passing the selection index in the `Editor::mutateSelectedText`
method callback
  - Storing all the selections content on many calls of
`Selection::copy` with `maintainClipboard = true` in a metadata
`selections` array
  - Handling clipboard with a `selections` metadata in
the`Editor::pasteText` method
:lipstick: Fix typo in pasteText method comments
Allow newer version of `nodejs`
Adds specs for multi selections clipboard handling
Don't use comment lines to determine soft/hard tabs.

Closes atom/language-php#24
Closes #1733
Upgrade to text-buffer@2.2.1
Merge remote-tracking branch 'origin/master' into cj-tabs-be-weird
Wordsmith the readme
fix io typo
This doesn't need to change.
Add mercurial directories to default list of ignored names

atom already ignored git and svn directories. It makes sense to ignore
mercurial (.hg) directories as well.
Apply @probablycorey's suggestions
Fix Windows build instructions
:memo: Some simple documentation fixes
Make atom build behind firewalls

This is to get `npm install` to work behind firewalls where `git://` is blocked.
+FreeBSD, -bullshit

Signed-off-by: Cthulhux <zeug@tuxproject.de>
Shift backspace keymap

Within windows build shift-backspace currently does nothing. Behaviour
untested in linux (perhaps linux.cson should be modified too?)
Upgrade to scrollbar-style@0.4.0
Upgrade to pathwatcher@1.2.4
Merge pull request #2071 from lee-dohm/doc-fix

:memo: Some simple documentation fixes