[Closes #149] Allow specifying an array of commands in the yaml.
[Closes #100] Use send-keys for multiple commands.

Previously multiple commands were run together using &&, preventing use
of multiple commands after SSHing into a server for example. Change the
behaviour to execute each command using send-keys.
Remove stray pry.
[Closes #154] Add option to call tmux wrappers or derivatives.
Fix an issue where the full tmux send-keys command wasn't being used.
Change the name for custom tmux command option to be more consistent.
Bump to 0.6.6.pre.
Remove duplicate describe block in window_spec
Refactor the testing of Window#build_panes

The previous specs seemed incomplete (i.e. when an Array is passed check
that Window#panes is not emtpy, and when a String is passed check that
it is an instance of Pane)

For the following two cases:

* The panes value is an Array
* The panes value is a String

I introduced the following specs:

* Check that the correct amount of Pane objects are being created
* Check that those created objects are returned by Window#panes
Ensure Window#panes always returns an Array

This is because it is treated like an Array in Window#panes? and in
lib/tmuxinator/assets/template.erb

Without this, the following YAML would fail:

windows:
  - vim:
      pre: "some_command"

and so would this:

windows:
  - vim:
    panes: "vim"
Merge pull request #157 from lmars/refactor-window-build-panes-method

Refactor Window#build_panes to always return an Array
Clean up some branching code by using presence
Merge pull request #163 from athal7/branching

Clean up some branching code by using presence
travis test matrix against multiple tmux versions
Merge pull request #164 from tony/travis-multitmux

Travis test matrix against multiple tmux versions
[#100, #165] Add support for send-keys and multiple pane commands and fix pre_window not working for panes.
Bump version to 0.6.6.pre.2
Remove stray pry require.
Bump version to 0.6.6.pre.3
Spellfixes

Grammar Nazi fixes.