Show all error details from JIRA

JIRA sends us errors as a JSON hash. We already showed all errors
contained in the array associated with the 'errorMessages' hash-key.

Some methods send errors in a sub-hash associated with the 'errors'
key. This commit shows them too.

Ref: https://github.com/gnustavo/JIRA-REST/pull/1
v0.007
Update README
v0.008

  [Changes]

  - Show every detail in JIRA error messages. Some of which weren't being
    shown before. (Thanks to Michael Kröll for the tip.)
Use JIRA default value for maxResults

If not set, JIRA uses 50 by default.
Fix the search iterator

It was all wrong, based on wrong assumptions I infered from the
documentation. I was able to understand it from this page:

  https://developer.atlassian.com/display/JIRADEV/JIRA+REST+API+Example+-+Query+issues

Also, now we defer the first POST(/search) request until the first
invocation of the next_issue method. The set_search_iterator method
doesn't POST anymore.
Check PUT and POST 'value' argument

It's easy to forget about the 'query' argument (which is the second one)
and pass the value as it instead of as the third argument.
v0.009

  [Fixes]

  - Fix the set_search_iterator/next_issue pair of methods.

  [Changes]

  - The iterators now use JIRA's own default (which is 50) when the
    'maxResults' argument isn't set. Previously our default was set to 256.
Show error details from the JIRA REST API too
Merged from upstream