Change TODO documentation from reST to Markdown

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
Update TODO to Markdown syntax.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
Standardize on two-space indented * for bullet lists in Markdown

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>