Improve method of writing analog data to connection

[jwoolston]

See #106.

Currently, the only times we write out data are when switching channels, at the end of sampling and while waiting for a sample to complete. In the case of waiting for a sample to complete, at higher sample rates this condition is never met.

An overall better solution should be found.

[ejberry]

Causes issues for sampling at high speeds. See #152 .