Added Metadata infrastructure

[alcides]

Addresses #30.

How to implement:

• Decorators need to accept a metadata dictionary, and return the new metadata dictionary.
• When decorators are being applied for each function, the new metadata is passed to the next decorator.
• Between function definitions, the metadata dictionary is also passed on to the next one.
• Metadata needs to be passed on to the synthesis procedure.

[alcides]

@eduardo-imadeira What do we want to call "syn_ignore", now that the old "ignore" is remove?

hide/hiding?
ignore/ignoring?

[eduardo-imadeira]

@eduardo-imadeira What do we want to call "syn_ignore", now that the old "ignore" is remove?

hide/hiding? ignore/ignoring?

I like having the 'syn' as the prefix of the decorator. But 'hide' is probably a better name than 'ignore', and is also shorter

[alcides]

But then it's inconsistent with minimize (syn_minimize) and the others in the family, no?

With namespaces, we could put them inside a module, and import the module on the top. But that's probably for after your thesis.