Move harness timeout to a <meta> tag.

To ensure that external tools can set useful timeouts for tests,
move timeout specification from setup() function to a <meta>
element with the format:

<meta name=timeout content=timeout-in-ms>
fixup! Move harness timeout to a <meta> tag.

Update documentation.
fixup! Move harness timeout to a <meta> tag.
Move to dual timeout for overall harness and multiplier for tests.

Switch to <meta name=timeout content=long> to specify a longer
timeout for a whole file.

Allow a timeout_multiplier to be supplied for individual tests so that
slow hardware can also increase the timeouts here.
Make tests not timeout by default, but run until the harness timeout and get a status of timeout.
Merge pull request #41 from jgraham/meta_timeout

Move harness timeout to a <meta> tag.