Many enhacements for the lua bindings

Load module and cast core instance at startup
Requires latest valabind.
Add RCore::ncast api
Use pkg-config everywhere to fix lua plugin build
Fix install path for lua bindings
Export RCore instance to #!lua shell
Example:
  #!lua
  print(c.assembler.bits)
Handle '!' and '.' commands in #! prompt

'!' : used to run system commands
'.' : used to interpret a file