Add multiple calculations of variance of tau

[lo-co]

For the purpose of calculating uncertainties, we want to calculate the variance based on chunking portions of the data. A description of Allan Variance is found here:

https://en.wikipedia.org/wiki/Allan_variance

[lo-co]

This has been added to the VI CRD Cells::Retrieve Taus. It will be written to file but not given a visual cue (i.e. it is not in the http data stream).

In conjunction with all of this, we have placed the data in the CRD Cell Data::Serialize -Text - it will be placed in the last portion of each cell data string in the text file - and have adjusted the VI CRD Cell Data::Generate Unique Header to reflect this in the header. The data written will be the standard deviations at different "chunk sizes"; this is the number of points that will be aggregated for a new point. The data will be aggregated initially in the following chunks:

• 1 (this is just no aggregation and is actually written to the file as the standard deviation for the current tau calculation)
• 5
• 10
• 25
• 50
• 100
• 250

This currently hard coded and there is no configuration parameter to set it by. In the file itself, the header entries will be _av5, _av10, _av25, _av50, _av100 and _av250. Once again, the standard deviation currently written represents the value that would be written under _av1.

The chunk size has different meanings depending on the laser repetition rate. For 1 kHz repetition rate, 5 would represent an average of 5 data points over 5 ms, 10 would represent 10 data points over 10 ms, etc, etc. For a 2 kHz rate, the period reflected would be half of these.