remove $unboundFn by improving lexer/parser

[IgorMinar]

currently the lexer will tokanize a.b.c() as a single token and return a getterFn that has c fn prebound to a.b. This was done to simplify the implementation of the parser and improve performance but it results in certain issues (e.g. watching a fn reference must be done via $unboundFn, see 7da2bdb).

It would be better if the lexer tokanized a.b.c() as a.b, ., c, where the . token would represent method invocation which parser would recognize and execute c in the context of a.b