add support for external generators

[eu-ch]

Hey @dromer, this is the external generator feature we've discussed earlier.

[dromer]

Cool! from first look it seems alright.

I'm not 100% yet on calling the abstract class Compiler. Since atm this specific class is only used for Generators.
So maybe it should be called Generator instead :#

CompilerResp is used in various places where objects have a compile() method though. So I think I named it this because of that.

What do you think, should we name this specific group of classes Generator? I think it would be more explicit.

[dromer]

btw I'm also going to move the Meta types to the new hvcc.types section :)

[dromer]

ok, I made these changes, please adjust the code so it fits again :)

Also please add the feature to the CHANGELOG.md !

[eu-ch]

ok, I made these changes, please adjust the code so it fits again :)

Thanks, will do later today. Also, please make up your mind regarding ‘-G’ argument, so I can change in code and docs. Alternatively, I can omit the short arg in favour of a long ‘--ext-gen’.