Suppot parsing bulit-in keywords

[WindSoilder]

Currently some keywords are missing in this parser:

• source (Should we set it as a keyword?)
• source env (Should we set it as a keyword?)
• export env (Should we set it as a keyword?)
• plugin use
• overlay use
• overlay hide
• overlay new
• try
• export module
• export alias
• export const
• export extern
• export def
• export use
• use
• extern
• hide (not sure about this either)
• module
• const