Add field for compiler flags to language version data

[kazk]

See #65

[hobovsky]

Is a field just for flags enough? Is compilation always controlled by flags of single command invocation? I mentioned command line deliberately, in case compilation and invocation were more complicated, consisted of more than one command, etc.

[kazk]

It all depends on the language, so we'll adjust as we go. I made language pages data driven so that we can just edit the source data to get 50+ languages pages with consistent appearance. We'll adjust the fields as necessary because it's difficult to know beforehand.

I might just end up having generic description/notes.