Integrate MIB Domain Specific Language into pic12 build process

Closes #36.

Removes the need to manually create command_map.asm files specifying mib endpoints supported by pic12 application modules. Instead the modules are described using a simple DSL, which is parsed and used to generate the command_map.asm file.  The MIB DSL supports file inclusion and variable definition so you can define well_known features and commands by name and refer to them in all mib modules, rather than having to use potentially volatile numerical identifiers.