Build universal binary

Allow colors to be generated and used in a Swift Package (via @youjinp)

Added -access flag to specify the access level for the generated code. Possible values are internal (default) and public.

Added a -mode flag to generate Swift code which either references the generated Asset Catalog (-mode asset-catalog) or uses dynamic colors instead (-mode dynamic-color).

Command output is now colored

• Swift file is not touched if its contents haven't changed

• variables can now have custom opacity
• added support for single line comments

• added support for RGBA values
• added support for specifying a color space
• existing asset catalogs are no longer overwritten by default