Adding support for number pattern param to to_number() built-in.
Added end-to-end tests for to_number() with pattern string.  Fixed serialization in ToNumberFunction.
Merge pull request #77 from elilevine/master

Added optional number pattern param for TO_NUMBER() built-in.
In TO_NUMBER, set EMPTY_BYTE_ARRAY and return true if input does not match pattern.  Add external documentation for TO_NUMBER.
In TO_NUMBER, small tweaks to ToNumberFunction.evaluate()
Merge pull request #78 from elilevine/master

TO_NUMBER external doc and minor change to ToNumberFunction.evaluate() per @jtaylor-sfdc's request.