Disable automatic switch of line numbers

Fixes #296
Revert numbers.vim causing relative numbering issue
Externalizing and improving search configuration
Merge pull request #301 from lfilho/insensitive-search

Externalizing and improving search configuration
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Externalizing and improving search configuration
  Revert numbers.vim causing relative numbering issue
  Disable automatic switch of line numbers