fix ES5 build to run test suite in nashorn

[andrew-coleman]

Changes made to the es5 build and polyfills to get jsonata-es5.js up to scratch for running the test suite in Java Nashorn. This is representative of a barebones ES5 implementation.
Most of the tests now run under nashorn with the exception of:

• tests involving multibyte unicode strings (might need extra polyfills here)
• case insensitive regexes (for some reason)
• base64 encode/decode functions

resolves #287 (hopefully)

[coveralls]

Coverage remained the same at 100.0% when pulling fa84555 on nashorn into bdafec2 on master.