Log Message:
Update to 1.2.1

Changelog:
tig-1.2.1
---------

Incompatibilities:

 - Move manual and man pages to doc/ directory and rename AsciiDoc files
   to have .asciidoc as the extension to make them render on GitHub.

Improvements:

 - Show blob sizes in the tree view either as bytes or using binary unit
   prefixes. Example: `set show-file-size = units`. (GH #163)
 - Reduce main view memory usage and startup time, especially when revision
   graph rendering is disabled. (GH #160)

Bug fixes:

 - Fix submodule-related setup to check for non-zero return value from
   setenv(). (GH #188)