Fast-plotter

Fixed
- Bugs in post-processing modules, PR 29 [benkrikler](github.com/benkrikler)

Added
- New post-processing command to reshape outputs of fast-carpenter from PR 28 [benkrikler](github.com/benkrikler)

- Many changes from PR 26 [benkrikler](github.com/benkrikler)

Fixed
- Bugs in the way overflow bins were handled and step-lines were drawn by padding. Impacted error bars as well as produced weird plotting artefacts.

Added
- Extend unit tests
- Variable interpolation within the config files and using variables which can be passed from the command-line
- Y-limits based on plot-margins: pass a float with a percent sign after to limit configs
- Control over the display of under and overflow bins from the config file
- Ability to give specific colours for individual bands in the plot
- Option to control how errors are calculated: sqrt of sumw2 or sumw / sqrt(n)

- Many changes from PR 13 [benkrikler](github.com/benkrikler)
Added
- Error bands in ratio plot on the expected R=1 line and the error markers
- Control over the colour pallete from the config file
- Control over the figure size
- News command-line options to make multiple image types (e.g. pdf and png) from a single command invocation
- This CHANGELOG was added

Changed
- Datasets can now be ordered, which only affects the colouring; they're still stacked according to total integral
- Fixes for using weighted events for data: use the dataset_col and data regex, as opposed to checking for NaNs