Mulensmodel

* Coordinates.v_Earth_projected() added
* Event.get_ref_fluxes() - fit_blending option added
* Model.get_ref_fluxes() - fit_blending option added
* Utils.velocity_of_Earth() added

* new install,
* Model.plot_trajectory() arrow_kwargs added,
* ModelParameters.is_finite_source() added,
* source plotting functions added: Event.plot_source_for_datasets(), Model.plot_source(), and Model.plot_source_for_datasets();
* satellite_skycoord keyword in Model.plot_magnification() and Model.plot_trajectory() added,

Model.set_magnification_methods() - *source* parameter added. Hack session examples.

Major changes as compared to previous release are implementation of Lee et al. 2009 for finite-source point-lens with large rho and extended binary source capabilities.

In detail:
* 1.5 -> 1.6 MulesData.plot() added; Model.get_residuals(..., data); Model.plot_residuals(... show_bad); Model.fit added
* 1.6 -> 1.7 Model.plot_magnification() and plot_lc() - additional keywords
* 1.7 -> 1.8 Fit.update(); Model.magnification(..., separate); Model.magnification() flux_ratio_constraint parameter can be string; Model.set_source_flux_ratio(None); Model.set_source_flux_ratio_for_band(); PointLens.get_point_lens_uniform_integrated_magnification();PointLens.get_point_lens_LD_integrated_magnification(); 2 new magnification methods: 'finite_source_uniform_Lee09' and 'finite_source_LD_Lee09'

Binary sources - basic functions work properly. Also pi_E added in mulenssystem.py.