Fast-plotter

Added
- Postproc: Control error calculation method and switch default for datacard inputs, PR 68, [DBAnthony](https://github.com/DBAnthony)

Fixed
- Postproc: Fix merge's sort option, add CLI logging controls, PR 62

Fixed
- Postproc: Fix default value for value_cols on command line, PR 60, [DBAnthony](https://github.com/DBAnthony)

Fixed
- Postproc: Built-in command-line help, PR 59

Added
- Postproc: Option to control sorting during merging, PR 57 [snwebb](https://github.com/snwebb)
- Postproc: Built-in command-line help for available stages, PR 54

Fixed
- Postproc: Make specification for value columns more rigorous, PR 55 [DBAnthony](https://github.com/DBAnthony)

Fixed
- Travis deploy to pypi, PR 52