Implemented astropy/astropy#933 and astropy/astropy#945. Created AsyncBase class for general async query. Updated relevant tests and docs. Also reorganized vo docs as discussed in lpaioro/astropy#3.
Made changes to doc as per astropy/astropy@6f7888b
Applied comments from Tom R.
Fixed Async classes examples.
Merge pull request #1354 from pllim/vo-conesearch-coord

VO Cone Search -- 2 feature requests, SAMP doc prep