Store custom templates in ApplicationSupport

[AliSoftware]

The idea of this feature would be to:

• Create a swiftgen template subcommand that could:
  • with no parameter: list all the installed templates in ~/Library/Application Support/SwiftGen/templates
  • --add FILE copy FILE into ~/Library/Application Support/SwiftGen/templates to install it as template
  • --open: Opens ~/Library/Application Support/SwiftGen/templates in the Finder
• Add an option parameter to all swiftgen subcommands to specify template by name
  • The option flag will be something like --templateName NAME / -n NAME
  • It will search for a template named NAME.stencil in ~/Library/Application Support/SwiftGen/templates first
  • If not found, It will search for a template named NAME.stencil in the bundled templates (installed in TEMPLATES_RELATIVE_PATH)

This will allow people to store/manage/use their SwiftGen templates in an easier way, instead of having to use the full path with --template each time. Note that the --template option will still work, and using both options should lead to an error.

See also #31 (comment)

[AliSoftware]

Also note that --template will now default to nil and the value having a default will now be --templateName instead.
For example, for swiftgen colors, specifying neither --template nor --templateName would default to the same as using --templateName default

The positive side effect that this would have is that people would be able to simply store their preferred default template for swiftgen colors simply in ~/Library/Application Support/SwiftGen/templates/colors-default.stencil and it will be picked by default instead of the one bundled with SwiftGen. This way, no need to specify --templateName each time if you have your own custom default templates!