update repr of ICRS
added TODO, updated representations
added mixed quantity list example
add todos, remove copy test
took a first stab at adding more detail to designing new coordinate systems docs
updated to use cartesian representation
typo
added back cartesian shorthand
added TODO and updated icrs
argh, another typo
added many TODO's to index
no idea if matching will change with skycoordinates, added TODO
minor change to separation example
updated Sgr example
update sagittarius example page
comment
updated doctests in transforming
Merge pull request #21 from adrn/coordinates-ape5-doctests

Update doctests
Moved APE5 API tests for SkyCoord to the right place
Add SkyCoord.to_string() method from original coordinates