Ported PID controller from telegraph to diminuto.

git-svn-id: svn://graphite/diminuto/trunk@539 5dfbf39a-1452-0410-8a97-9e58fedde8e3
Updated unit test.

git-svn-id: svn://graphite/diminuto/trunk@540 5dfbf39a-1452-0410-8a97-9e58fedde8e3
Changed datum enum to use module prefix.
Minor tweaks to controller.
Adding tree partial implementation.

git-svn-id: svn://graphite/diminuto/trunk@541 5dfbf39a-1452-0410-8a97-9e58fedde8e3
Adding UNTESTED containerof and offsetof.

git-svn-id: svn://graphite/diminuto/trunk@542 5dfbf39a-1452-0410-8a97-9e58fedde8e3
Still working on tree.
Removed unneeded private header file.

git-svn-id: svn://graphite/diminuto/trunk@543 5dfbf39a-1452-0410-8a97-9e58fedde8e3
Tree compiles.

git-svn-id: svn://graphite/diminuto/trunk@544 5dfbf39a-1452-0410-8a97-9e58fedde8e3
CHeckpointing tree while working on unit test.

git-svn-id: svn://graphite/diminuto/trunk@545 5dfbf39a-1452-0410-8a97-9e58fedde8e3
Initial tree insert unit testing passed.

git-svn-id: svn://graphite/diminuto/trunk@546 5dfbf39a-1452-0410-8a97-9e58fedde8e3