fix: validate compiler arguments

[PK1A]

Not sure if this is JavaScriptish way of doing those checks, but at least arguments are verified now. I've bumped already several times into obscure err messages from a compiler when not providing a second argument so I really like to fix this one, this way or another.

[PK1A]

One more remark - this PR changes how fatal errors are communicated by throwing an exception. This partly solves #61

[benouat]

I might be the only one, but I am still not in favor of this change...
To me, if not provided it should silently fallback to "anonymous".

With this change, if you want to play from a pure browser point of view, with template content coming from <script ></script>, we are simply forcing the user to put this anything/anonymous parameter, which is bad.

I understand that it is really needed for errors purpose when used server-side, but still ....

[PK1A]

Finally I've merged this one as today the second argument is mandatory - compilation will fail if it is not provided. Before this commit it was failing with a cryptic error message (bumped into it again today...). Now we've got a clear error message without any functional change.