Remove extraneous comments. Clean up global vars.

- Refactor global vars to be more consistent across the file
Remove extraneous comments from toggle on section
Refactor sidebar creation code

- Move sidebar creation code into function call parameterized on sidebar size
  and desired location
Correct and refactor vimroom options settings

- Correct global options to use "set"
- Correct local options to use "setlocal"
- Moved settings into function calls to reduce cruft in the main method
Move sidebar creation into CenterScreen function
Refactor navigation mappings

- Remove <unique> tag in the mappings
- Add <buffer> tag to the mappings
- Remove try/catch statement, it's no longer needed with <unique> removed
- <unique> was removed because there's already a check to see if
  g:vimroom_navigation_keys is present so it's a redundant to still check if
  those keys are already mapped.  Instead it's made a buffer local mapping with
  the assumption that if the user didn't want it remapped, that global option
  would be set to 0.
Refactor logic for hlgroup background colors

- Remove global background variables g:vimroom_guibackground and
  g:vimroom_ctermbackground - these were hardcoded with values which didn't make
  sense if your editor used a different background color or switched color
  schemes frequently
- Determined background colors based on the current value of the Normal
  hlgroup
Moved t_mr and fillchars to SetGlobalOptions
Merge branch 'toggle_on'