Explain where functions.py comes from

Add a note to the docstring. Sorry, @moskytw
Lazy resolve all _as calls
fields really should be extra_fields
Rename _get_query_string() to query

Matching Django QuerySet's convention
Disable __getattr__ proxy to RawQuerySet
More cleanup
Simple slicing implementation

A (kind of) working implementation of slicing. The problem here is that neither MySQL and SQLite supports OFFSET without LIMIT, which is troublesome. Some choices here:

1. Set a default for LIMIT if necessary. This is the default implementation (using sys.maxsize for a "very large integer"), but is not without problems. One of those is that sys.maxsize may not be enough -- MySQL supports up to 2^64 - 1, for example, but sys.maxsize is only 2^63 - 1 (because it's signed). There might be problems in cases that sys.maxsize is too large and causes overflow on the database side.

2. Let the user figure a way out. MoSQL generates SQL fine with or without LIMIT, so we can just let the query die if the user does the wrong thing. Kind of harsh in my opinion though.

3. Do some crazy database detection at runtime. Django supports only limited database versions, so we actually can exhaust all possible cases, and provide sensible defaults as needed. But might be a bit ugly? Maybe we can take a peek into Django's implementation to get an idea.

Need to sit on this for a while to decide.
Fallback when lazy model-loading fails

When join's lazy model-loading fails, try to treat it as a plain table name instead of quitting
Add some documentation
Fix extra_fields -> _as conversion

Obviously I forgot to commit some changes. This should fix the failing Travis CI builds.
Use a dict to store select parameters

This cleas up the code a bit, and makes it possible to check whether the clone is complete.

Fix #3
Add a test for param keys
Use Django's implementation to resolve LIMIT
Merge branch 'slicing'

Fix #5
Cleaner JOIN param formatting
Use dict comprehension to simply formatting

We won't support Python 2.6 anyway (since it'll be dropped by Django 1.7)
Riase minimum Django version to 1.4.2 for six
Fix typo
Bump to v0.2 and add CHANGELOG
Make a deepcopy of params before generating query

Fix #10