Refactored raspivid to allow user to pause and restart captures
to the same file using a timer, keyboard or signals. Camra can be
started in record or pause state.

New options -s, -k, -td, -i

Updated docs to reflect new commands, updated raspivid version to 1.3.3
Merge pull request #104 from JamesH65/video_pause

Refactored raspivid to allow user to pause and restart captures