added some more detail about quantity objects
wrap line
check in sketch from google doc
initial outline
added coordinates system description paragraph
merged with @adrn's paragraph
added some more to introductory paragraph
Edits to coordinates intro paragraphs
minor grammatical things
add some text for input parsing section
Added tranformation section
added distance section on coordinates
Merge 'adrn/coordinates' into 'eteq/coordinates' resolving conflicts

Conflicts:
	astropy.tex
add galactic coordinates references
revisions
Small tweaks from @adrn's changes
update angle section to be less documentation-y
Demitri's comments/edits for coordinates section.