GRID-236 change POST body signing behavior

- max_body defaults to 128kb
- if post body to sign is larger than max_body truncate to max_body
instead of throwing an exception
Merge branch 'master' into GRID-236-post-body-signing-changes
update max_body to 2048 as per mastevens
Merge pull request #2 from akamai-open/GRID-236-post-body-signing-changes

GRID-236 change POST body signing behavior