🚀 Allow custom themes to be defined as light themes

[kidonng]

Currently delta determines whether a theme is a light theme by checking it against a fixed list. This causes all custom themes considered dark themes, which is inconvenient as users have to supply a extra --light flag to make light themes work as expected.

Proposal: In additional to the fixed list, if a theme has "light" in its name, then consider it a light theme. This is not perfect but I don't know any dark theme having "light" in their name, so it should be fine :)

[dandavison]

Hi @kidonng, yep good call, this sounds reasonable, will do!