#228 - implement basic plumbing for plugins

This functionality is to be considered in 'alpha' state. The aim is to
enable basic extensibility outside of the Packages/Vintageous directory.

To that end, a PluginManager class has been created to gather date needed
to encode commands as Vintageous expects them.

As a sample implementation of a plugin, check out:
https://github.com/guillermooo/Vintageous_Plugin_Surround
#260 - improve pasting linewise onto visual line selection
improve handling of user input; edit changelog
Added tag 1.4.1 for changeset af01059bd5bd
Fix repeat of insert

Fixed the issue that repeat by '.' after inserting characters by 'i'
doesn't work.
Fix repeat failure of insert with delete

Example: iFOOBAR<right_delete><esc>.