Add URL/URI Helper Functions

[jhorbulyk]

As discussed in #103

[coveralls]

Coverage remained the same at 100.0% when pulling 4897027 on elasticio:add-uri-helper-functions into 00d36d0 on jsonata-js:master.

[andrew-coleman]

Hi Jacob, I note from the Mozilla docs that these functions could throw a URIError for malformed URI sequences. Please could you catch these an re-throw a jsonata error code? This helps maintain conformance across different jsonata implementations (Java & Go that I know of). Thanks!

[jhorbulyk]

@andrew-coleman Do you have any preference for one single jsonata error code or should I add an error code for each of the 4 functions?

[andrew-coleman]

One error code is fine. You could add the function name as an insert into that error. Thanks.

[jhorbulyk]

@andrew-coleman Updated.