Add SchemaDocumentError to __all__, instead of 2x SchemaDocument

From what I can tell, it was intended to include SchemaDocumentError
in __all__, but instead two instances of SchemaDocument were listed.
To help clear it up, I also sorted __all__.

Now, SchemaDocumentError can be directly imported. Since this class
is the parent of all schema document errors, you can use this class
in a try/catch to pick out any schema document error.
Minor formatting of README
Fix for dotted dicts and pymongo 2.7

Provide fix for dotted dict and i18n dict. There was huge __getattr__ protocol violation in those classes thar caused problems with new versions of pymongo c extension
Restore Python 2.6 compatability
Another python 2.6 compatability fix
Merge pull request #179 from last-g/fix-dotted-dict-upstream

Fix for dotted dicts and pymongo 2.7
Merge pull request #178 from davidjb/patch-1

Minor formatting of README
Copy-paste misstype
Merge pull request #180 from last-g/fix-dotted-dict-upstream

Copy-paste misstype
Merge pull request #171 from wrhansen/master

Add SchemaDocumentError to __all__, instead of 2x SchemaDocument
Merge branch 'master' of https://github.com/namlook/mongokit