multiwavelength/gleam: Initial release of gleam

Initial release of the gleam software. Main features include: Process large numbers of sources in batch mode. Jointly fit lines located close together, report upper limits and identify lines without spectral coverage. A single configuration file for an entire project, which you can use to customize the fitting for specific telescope/instrument configurations or even single sources. Human-readable YAML configuration file, in which units can be specified. Plots of an entire spectrum with the line fits, as well as plots for each individual line fitted. Well integrated with Astropy, which enables the use of units and fits tables. Uses LMFIT to perform the fitting and report errors on fit parameters. Simple installation with pip