Postprocessing

[FCMeng]

• Need a dict key to indicate if the spectra are epsilon2 or cross section.
• Need output for different polarization directions, current implementation is averaged.
• Need a key for the site index.
• Need a better way to match the site index between OCEAN and other codes.The site index for all elements in OCEAN starts from 1. For example a system has three Ti sites (all equivalent) and three O sites (all equivalent). For other codes other than OCEAN, the site would be Ti_000 and O_003. For Ti in OCEAN, it would be absspct_Ti.0001_1s_0?, absspct_Ti.0002_1s_0?, absspct_Ti.0003_1s_0?; for O in OCEAN, then it would be absspct_O.0001_1s_0?, absspct_O.0002_1s_0?, absspct_O.0003_1s_0?, which leads the site index quite different compared to other codes.
• Not sure if we want to store/parse the structure in the output.