Keep body fields in the order they were provided in.

Some (non-standard?) APIs seem to rely on the order of fields in requests.
Using the order keys come out of the HashMap is suboptimal in this case, so
I've added a list to track the original order.
Merge pull request #33 from tcoxon/ordered_fields

Some APIs require fields in a particular order.
implementing head, options and closing #20
Merge branch 'master' of https://github.com/Mashape/unirest-java
updating user agent;
fix test
[maven-release-plugin] prepare release unirest-java-1.3.11
[maven-release-plugin] prepare for next development iteration
readme
readme
fixing field()
readme
temp fix
[maven-release-plugin] prepare release unirest-java-1.3.12
[maven-release-plugin] prepare for next development iteration
Increase max connections for async client; closes #34
[maven-release-plugin] prepare release unirest-java-1.3.13
[maven-release-plugin] prepare for next development iteration
version
fixed critical bug