Parse decimal and hex numbers correctly.

Fixes two bugs:

* '4a' lexed to token: 4 & token: a - Now correctly a lex error.
* Failed to lex hex numbers.

Octal is not supported in JS 5.1, though apparently it was in earlier versions of JS.

Have been trying to setup a testing framework but CommonJS requires are my enemy. Also just learning node. We should probably tweak file structure to have src and test trees, and agree on filing naming conventions. I'm not a big name of capitalized letters in file names or package names.