AST based parser

Almost complete ES5 grammar, few missing basic things:

* Function statements (functions inside functions. Not `f = function() {}`
  which is covered by function expressions)
* labels
* `for in`

Furthermore, for now identifiers and string literals only contain the first letter.
They will contain pointer+len field; deferring until the VM internals are redesigned.

Manual tests cover all constructs and check a manually inspected serialized AST.
They allow safe refactoring of the parser until we can actually execute ECMA 262 tests.

Most ECMA 262 tests are also parsed without errors, although I didn't check whether
the AST makes any sense. Some ECMA 262 tests are skipped because they rely in yet
to be implemented grammar.
Merge pull request #46 from cesanta/ast

AST based parser
Add `amalgamated_v7` target

Otherwise we cannot spot build failures caused by incorrect amalgamation
order and similar issues.
Fix associativity of binary expressions
Merge pull request #47 from cesanta/make_amalgamated

Add `amalgamated_v7` target
Merge pull request #48 from cesanta/fix_associativity

Fix associativity of binary expressions
Make binary parser boilerplate slightly more terse
Merge pull request #49 from cesanta/parser_style_fix

Make binary parser boilerplate slightly more terse
Added sketch for VM