Merged my own code with Path Tools pluing

- Removed the CopyFilePathCommand becasue there is already a command in
Sublime Text that does this (copypathcommand)
- Added proper handling of is_enabled so the commands are disabled if
the current file don't have a name/path yet
- Changed how to get the file directory by using os.path.dirname instead
of splitting
- Updated the tab context menu so that all copy commands are vailable
from there
- Added regular context menu for the insert commands
- Added menu under Preferences > Package Settings for users to see
default key bindings and open the user key binding file for overriding
the default ones
- Added separate keymap files for Windows, Linux and OSX
- Updated the readme file to reflect the changes