Refactor tree for non-recursive automake (mostly)

* libtap moved to t/libtap
* libgdmaps/t moved to t/libgdmaps
* all recursive source subdirectories have had their Makefile.am
merged to the top level in non-recursive style.
* testsuite-related subdirs (t/ and below) remain recursive
because (a) it makes testsuite dependencies far easier to deal
with and (b) testsuite Makefile.am's tend to be very complicated,
which makes a mess when integrating them into a non-recursive top
level Makefile.am
* includes other random improvements to the build/test/qa stuff
minor type nits for some systems
Fix some outdated info in the plugin API docs