This changes the base16 theme back from #RRGGBB0f to #RRGGBB00,
reverting part of #934. That PR used the 0f encoding to produce ANSI
escape sequences 30-37 and 40-47 rather than 38;5 and 48;5 which require
256-color support. Unfortunately, it resulted in base16 using the wrong
colors becuase ansi_term does not support the bright variants (90-97 and
100-107) so it simply mapped them to the non-bright colors.
This PR makes combines the 00 and 0f alpha encodings into 00, and makes
them use the Color enum for the first 8 colors and Fixed otherwise. This
means the ansi-light and ansi-dark themes will work on terminals without
256-color support, and base16 will render bright colors correctly.
This changes the output color of the grid and the line numbers to use
the "gutter" foreground color defined in the Sublime `.tmTheme` files.
Sublime Text does the same.
Note: we could go one step further and also extract the "GitGutter"
colors from the themes. These could be used instead of red/green/yellow
to signify Git modifications. The problem is that they are quite a bit
harder to extract from the syntect `Theme` object.
closes#178
