First commit of JWB's vib-EELS code

[irrotational]

Adds vib-EELS functionality to OptaDOS

Main additions:

phonon_eels Module

Provides functionality for both aloof and impact vib-EELS calculations, namely:

• Impact EELS loss spectrum
• Aloof EELS loss spectrum
• Oscillator strength tensor
• Low-frequency dielectric function
• Polarizability

Introduction of the OptaDOS Data (.odd) file format

.odd files are read by the read_odd module, and are currently only used for vib-EELS tasks. They allow the block-specification of key quantities, like partial charges and atomic displacement parameters.

odplot.py

The odplot.py plotting utility is provided (in optados/python), for plotting the output(s) of vib-EELS calculations

Other

• PhonPrep.py preprocessing utility (in optados/tools) for extracting essential vib-EELS quantities from .castep files
• Test runs for NaCl and hBN have been added to the test suite
• Several vib-EELS examples in optados/examples
• Documentation has been updated to include relevant vib-EELS background theory, and examples