Modifies the GET behavior on list resources to adhere to HTTP standards when the If-Modified-Since header is present

Previously, eve would return a partial document list if only some documents had been modified since the time present in an If-Modified-Since header. However, the correct response should be to return all documents (200) or no documents (304) only. Returning a partial set is not an option. See issue #190 for more information.

To implement this fix, I do a preflight query leaving req.if_modified_since in place with a limit of 1 sorted by date. (This query effectively answers the question "has anything been modified since this date?") By placing this check in methods/get.py, the same 304 response behavior will exist regardless of data layer.

I would prefer, however, to entirely remove the code in io/mongo/mongo.py that checks for req.if_modified_since since I'm not sure if other HTTP verbs/methods rely on req.if_modified_since. But to do so, I'd have to modify the where argument of the request, and since the query arguments aren't parsed before the data layer and since multiple where argument formats are allowed, this would have been difficult or at the very least redundant. (Redundant if I parse the where clause, modified it, re-stringify and then the data layer would once again re-parse it.)

On that note, I'd suggest moving argument parsing out of the data layer and into utils.py/parse_request(). By placing argument parsing in the data layer as currently implemented, the possibility exists for data layers to interpret arguments differently. I imagine the preferred response is to support and enforce the same query syntax regardless of the data layer. Issue #194 has been opened to relay this request.
Merge pull request #197 from petrjasek/develop

Fix _links.self.href for additional lookup requests.
Ditch Gittip for Gumroad.

This will allow for one-time only financial support.
Stack Overflow
Fix gumroad button class on secondary pages.
Eve Newsletter
Addresses #199.
Merge branch 'develop'
v0.2 release date.
Bumped version to 0.3-dev
v0.2 changelog typo
Extra entry point follows Eve 0.2 url rules.
Validation errors reported as dictionaries.

Validation errors are now reported as a dictionary with offending fields as
keys and issues descriptions as values. Cerberus 0.5 is now required.
For more information see:

https://groups.google.com/forum/#!topic/python-eve/E0A6YYq_h2c
Merge branch 'issue190' of github.com:joshvillbrandt/eve into joshvillbrandt-issue190

Conflicts:
	eve/methods/get.py
pre-flight call to find() updated to match 0.2 syntax
If-Modified-Since behavior as per HTTP specs
Merge branch 'joshvillbrandt-issue190' into develop. Closes #190.
Custom ID_FIELDs would cause update/insert methods to fail. Fixes #203.
Exclude etags from payload when concurrency control is disabled. Closes #205.
Document the etag exclusion when IF_MATCH is disabled.