[doc] improve index page
add support for PostGIS geography type
module reorg
[doc] more doc strings for types
add functions
remove function names for operator <-> and <#>
test module reorg
add comparators/operators (contains does not currently work)
[doc] display special methods
fix the contains comparator
more doc strings for comparator rshift and lshift
right and left comparators renamed to_right to_left
update README
[doc] comparator.rst renamed to spatial_operators.rst
[doc] change title of spatial operators chapter
[doc] more doc strings in comparator.py
[doc] more doc strings in functions.py
[doc] better intro to ORM tutorial
[doc] better intro to Core tutorial
[doc] Polygon type is gone