Update font patching documentation

Update reference to where fontpatcher.py is located
Improve battery support:

- Use dbus+UPower if available (code taken from kovidgoyal@7f73453 and
  refactored).
- Use any battery from /sys/class/power_supply: replace hardcoded BAT0/BAT1 with
  cycle.
- Use pmset.
- Use win32com.client with Win32_Battery object (code taken from an [SO
  question][1] and refactored).
- Use ctypes + GetSystemPowerStatus (from [the same question][1]).

Completely untested (only know that syntax is correct), will probably have to
hear replies from users to merge.

[1]: http://stackoverflow.com/a/21083571/273566

Closes #677.
Fixes #820.
Use CIE2000 to determine color distances, compute gradients in Lab

Slow
Use new script to regenerate dark_GREEN_Orange_red

Used command was

    tools/generate_gradients.py 22 58 94 52 --weights '60 15 10 2'

as earlier.
Also use CIE2000 in colors_find
Merge branch 'better-gradients' into develop
Fix test_local_overrides.vim test broken by better-gradient branch
Merge branch 'fix-vim-overrides-test' into develop
Add a way to omit computing colors for terminal
Refactor generate_gradients.py
Reverse JSON output and add trailing comma

Makes it easier to copy-paste output to colors.json.
Merge pull request #913 from ZyX-I/improve-generate_gradients

Improve generate_gradients.py script
Reverse the gradient in battery segment

Closes #910
Document how to create gradient colors
Use battery_full and battery_empty for displaying hearts

Red hearts for battery full are still more optimal in case white hearts are for
empty (though I do not understand why they have to be red). Cannot agree about
per cents though: red is better for empty then white is if there are no related
parts to compare.
Add two more colors to white_red gradient cterm colors

Picked up with

    tools/generate_gradients.py 231 223 216 209 196
Regenerate gui colors for white_red gradient

Command used to generate colors:

    tools/generate_gradients.py -C 231 255 223 216 209 202 196 --weights='1 1 1 1 1 1 3'
Merge pull request #914 from ZyX-I/better-battery-colors

Improve battery segment colors
Default line_percent_gradient to (light|dark)_green_gray gradients

dark_green_gray gradient was generated with

    tools/generate_gradients.py 70 247

. It is used for non-insert modes in the current window. light_green_gray
gradient was generated with

    ./tools/generate_gradients.py 148 250

. It is used for insert mode in the current window.
Merge pull request #915 from ZyX-I/better-line_percent_gradient

Default line_percent_gradient to (light|dark)_green_gray gradients