Add empty() to IOStream::Device and drivers
Allow thread yield during analog conversion wait.
Protect toggle and pulse.
Add weekday symbols and clean up epoch definitions.
Update benchmark run. Clean up CosaBenchmarkPins.
Benchmark run after latest updates.
Benchmark run after latest updates.
Check that empty() works
Make IOBuffer::empty virtual
Fix CosaIOBuffer testing of gets()

As recommended by Mikael.
Merge pull request #255 from jediunix/IOStream-empty

Add empty() to IOStream::Device and drivers