Add methods for drawing markers over sky image

[adl1995]

As outlined in this Jupyter notebook (https://github.com/adl1995/HIPS-to-Py/blob/master/examples/JPG_tile_draw_issue.ipynb), I have added two methods for drawing markers and lines over an all-sky image.

[coveralls]

Coverage increased (+0.1%) to 96.667% when pulling ea0233f04507d87d77b6798b9d142247773a42c3 on adl1995:tiles_markers into 60a5d95afb06be2511698cfdf335799d0dbc232e on hipspy:master.

[adl1995]

@cdeil Just updated. Please check.

[coveralls]

Coverage increased (+0.1%) to 96.667% when pulling 2153353a7c25f9894e9875eea18ed52e0d6ad779 on adl1995:tiles_markers into 60a5d95afb06be2511698cfdf335799d0dbc232e on hipspy:master.

[coveralls]

Coverage decreased (-1.3%) to 95.238% when pulling dbf189186e8f6c9310bf887bbe7c0c331641c459 on adl1995:tiles_markers into 60a5d95afb06be2511698cfdf335799d0dbc232e on hipspy:master.

[coveralls]

Coverage decreased (-1.3%) to 95.238% when pulling 12e065b6db71d3bc2049461c11ca4bccec029b6a on adl1995:tiles_markers into 60a5d95afb06be2511698cfdf335799d0dbc232e on hipspy:master.

[adl1995]

@cdeil I made the update, but now the grid lines from the second image are gone as well. Here is the updated notebook: https://github.com/adl1995/HIPS-to-Py/blob/master/examples/Draw_markers_plots_image.ipynb

[coveralls]

Coverage decreased (-1.3%) to 94.799% when pulling b9a4bafc93838326cbf110b3f1762a5c997af4ef on adl1995:tiles_markers into 7116cd8ef6134d4955103ba76462c7479e0a16fb on hipspy:master.

[coveralls]

Coverage increased (+0.4%) to 96.454% when pulling 9005878e851ee8f64ac498599bba8737a1fd83f4 on adl1995:tiles_markers into 7116cd8ef6134d4955103ba76462c7479e0a16fb on hipspy:master.

[cdeil]

@adl1995 - I think I know what's wrong. I'll merge now and fix in master and link to the fixup commit from here.

[cdeil]

I think with 524bb43 it should work properly. @adl1995 - Please try again with latest master.