initial support for tables (pipe and grid styles)
improve grid table delims
add support headers in grid and pipe tables.
support pipe tables without beginning and end column pipes
Adds support for simple and multiline tables.

Missing still: highlighting within cells, multiline headers.
support multiline headers
add support for orgtbl-mode pipe tables.

also, expanded table tests
Let YAML header end with ... in addition to ---
Merge branch 'tables'