add relative number

relative number sets the column index number to the relative distance up
or down from the cursor location.
add number toggle

number toggle is a plugin for relative numer that toggles between actual
index and relative index with <C-n> and toggles to the actual index when
in 'input' mode.
Merge pull request #25 from zachmokahn/vimrc_local

add relative number
Merge pull request #26 from zachmokahn/vimrc_bundle_local

add number toggle