Configurable colors, table formatting, support NO_COLOR spec

[deviaze]

Configurable colors and formatting

seal now respects the NO_COLOR specification.

New features in std/io/format

Added format.FormatOptions which you can pass to format.pretty and format(); pass it to format.defaults to override the behavior of print and pp.

These options now include these new features:

• print guidelines (automatically enabled when indent < 3)
• configurable number of spaces to indent over
• enable/disable printing metatables
• limit the amount of array elements shown
• enable/disable array indices (if you only care about seeing the values)
• max table depth after which the formatter stops recursing.

General formatter improvements:

• Formatter now prints function names when available and not equivalent to their table key value.
• Formatter now prints snowflakes around frozen tables.

New features in std/terminal

• terminal.background which gets the current background color of the terminal if supported. Might not be supported on all platforms/terminals.

Changes to std/io/colors

• colors.rgb which allows generating arbitrary terminal colors.
• colors.override enables or disables colors at runtime.
• colors.enabled checks if colors are enabled or disabled for whatever reason (NO_COLOR/etc.)