Pyp-beagle

- Fix pypi failure: specifying that the README is in Markdown format, otherwise pushing to pypi fails, see https://pypi.org/help/#description-content-type and https://github.com/di/markdown-description-example
- Bug fix: the marginal photometry plot was failing when the filter configuration file contained bands not present in the observations, but only computed for the models
- Added option to specify flux units for photometry
- Update README.md

- Read object redshift from the Beagle output file, so that pyp_beagle correctly deals with redshifts when provided in the prior catalogue; correctly plots masked regions read from the 'MARGINAL SED MASK' extension
- Correctly identify object ID from Beagle output file name
- Cosmetics improvements to the marginal photometry plot

- Introduced option to overplot on a photometric SED the maximum-a-posteriori (MAP) spectrum
- Exploiting the *args and **kwargs appraoches to simplify the passing of command-line arguments to the different classes

- Bug fix: file names of spectra and object IDs were not correctly matched

- Correctly dealing with lines not observed (i.e. negative fluxes and errors in the observed catalogue)

- Implemented option to print the values of observed and model fluxes on the plot
- Removed unused function
- Changed parser variable name
- Cosmetics: added dotted lines linking symbols in the plot to the line labels on the x-axis