Removing Python 2.5 from the Travis config since Jinja2 no longer supports it

The latest versions of Jinja2 no longer support Python 2.5 [[1], [2],
[3]]. Since Jinja2 is an integral part of Flask, this would also mean
that Flask no longer supports versions of Python prior to 2.6. Since
Flask no longer supports versions of Python prior to 2.6, plugins for
Flask do not need to support them either and so, the 2.5 Travis test
can be removed.

[1]: https://github.com/mitsuhiko/jinja2/pull/185#issuecomment-18098870
[2]: https://github.com/mitsuhiko/jinja2/commit/b89d1a8fe3fcbd73a8f4cebd4358eadebc2d8a9d
[3]: https://github.com/mitsuhiko/jinja2/commit/8bdc65d9e57d5c0da329bb88127d977bd58002e5
Fixed `__repr__` functions to work with Python 2.6 and above

In a Python 2.6 repl an exception is thrown when viewing instances of
the Filter, SearchParameters, and OrderyBy classes. This is because
the call to `str.format` in the `__repr__` method of each omits the
indexes for the arguments, which is a feature added in Python 2.7.

From the Python docs [7.1.3. Format String Syntax][1], "Changed in
version 2.7: The positional argument specifiers can be omitted, so '{}
{}' is equivalent to '{0} {1}'."

[1]: http://docs.python.org/2/library/string.html#format-string-syntax
Fix is_date_field for simple types

Having a simple type returned from e.g. a hybrid_property, an
`AttributeError` would be thrown from `is_date_field`. Fixed by checking
for the `property` attribute before accessing it. Added test case that
provoked the error prior to the fix.
Allow post/patch of nested submodels

Recurse into nested relationships and find/create models on post/patch
(previously threw TypeError: unhashable type: 'dict')
Merge pull request #228 from goodscloud/remove-jsonhttpexception-dependency

Revert "Adds a wrapper around abort function to add JSON Content-Type."
Merge pull request #217 from croach/python2.6-fix

Updated `__repr__` methods for several classes to work with Python 2.6 and above
Merge pull request #215 from croach/remove-python25-from-travis-config

Removing Python 2.5 from Travis config since Jinja2 no longer supports it
Notes changes due to previous commits.
support SQL-standard date/datetime functions

This allows setting date and datetime type fields to the values `CURRENT_DATE`, `CURRENT_TIMESTAMP`, and `LOCALTIMESTAMP` from the API, and translates that into SQL expressions that get evaluated by the database.

This allows client-side code to set a date or timestamp to current as seen by the server, in case the client computer's clock is incorrect.
Groups third-party library imports together.
Places current time indicators in a module-level constant.
Documents changes due to previous commits.
Changed for readability
pep8 fixes
Fixes issue 216.

Use query limit/offset on query instead of query result.
Merge pull request #225 from dnordberg/master-issue-216

Fixes issue 216: Paginated responses are extremely slow
Notes changes due to previous commit.
Merge pull request #220 from logandk/hybrid_setter_error

Fix is_date_field for simple types
Notes changes due to previous commit.
Decapitalizes issue descriptions in changelog for consistency.