Add setImmediate polyfill

#215

add paramsProcessor support to give application a hook to add general XHR param processing

#181
#182

Always set timeout property for error object

#176 by @lo1tuma

Add custom request header

#158, by @nysd

Check whether the number is valid in params in order to avoid Infinity

#152, by @kouhin

Prevent unsupported operation call

#154, by @nysd

Defensive code for fixing TypeError in browser

#150

Fetchr request stats collection/monitoring support

#148

Support for withCredentials option in XHR

See #149.

Invalid resource error handling

#146 by @narkq