Add :buffer Ex command

Mostly compatible with Vim. The incompatibilities are

 - There must be a space between the command and the buffer reference, even if
   that reference is a number. E.g., vim supports `:b4` but this command
   requires that to be `:b 4`.

 - A trailing `!` causes the command to not be recognized.

 - The buffer command behaves as if a trailing `!` had been added.

 - There is no completion support.
Add :buffers command

The output needs improvement. It doesn't include all of the information that
vim provides and the status bar doesn't support including newlines.
Improve output of :buffers command

The output contains the buffer number and has one entry per-line. As the
status bar output currently doesn't support including newlines, a new buffer
is created.
<C-6> and <C-^> normal mode commands
Missing synonyms for :buffer
Fix normal mode command `C` on part of a line

Previously, when operating on part of a line, `C` would move the cursor one
char to the left.
Merge pull request #486 from benarmston/vim2-fix-normal-mode-C

Fix normal mode command `C` on part of a line
Merge pull request #485 from benarmston/vim2-buffer-and-buffers-ex-commands

Vim2 improve buffer navigation
Reformatted the Parser and Steps data types 

Added legibility.
Merge pull request #488 from Cipherwraith/patch-1

Reformatted the Parser and Steps data types
Support for Meta and special key bindings for Vim2

This patch implements parsing and matching of events such as <a-c>,
<M-x> or <C-Left>.
Merge pull request #489 from bartavelle/master

Support for Meta and special key bindings for Vim2
Remove Yi.Prelude

Move utility functions from Yi.Prelude into Yi.Utils
Merge pull request #490 from fread2281/no-prelude

Remove Yi.Prelude