Bump version to 0.12.0
Bump version to 0.12.0

Changes since 0.11.0:
  * Implement maktaba#python#Eval, a polyfill for pyeval that works on
  vim versions older than 7.3.569.
  * Fix maktaba#path#Basename('foo') to return 'foo', not ''.
  * Improve JSON support to handle NaN and Infinity values consistently.
  * Fix IsCallable and IsEnum checking on 7.4.1875 and later.

google/vim-maktaba,malcolmr/vim-maktaba