Implement Agilent NWA and SR830 LIA. Write 'func' feature math->function for data explorer.

Write GPIB Implementations for two pieces of equipment:

- Agilent 8753ET transmission/reflection network analyzer. Features are limited:
-- Read/Write the frequency of continuous frequency output
-- Read/Write the power of output

- Stanford Research Systems SR830 digital lock-in amplifier. Features are very limite:
-- Read/Write the frequency and the amplitude of output

Write new 'math->function' feature for Data Explorer. Credit goes to Gregory Holloway.
- Calculate a function of a given coloum of data, keep in csv form.
- TODO: add support for numpy functions by using np.exp, etc. as input.
Add menu entry math->function to Data Explorer

The function.py file was written previously by Greg Holloway. Add the menu entry in Data Explorer to link to that feature.

Add line '*.py~' to .gitignore, in case files are edited with gedit, etc.
Change version to 2.0.1a

Kaveh Gharavi is now the maintainer.