feat: impl any <> interface conversions with accepts_interface option

[technicallyty]

ref: #5

• implements functions to handle/parse options (options.go)
• changed fieldGoType to return an interface so we can return either the string or GoIdent. This is kinda messy, and unsafe in some cases, however this allows us to just stick the interface in g.P(goType) and have it just work.
• modify the newFileInfo function to search for options in the message fields, and overwrite fields to use the interface type as their goIdent.