Add probable starter attributes, fixes #32

[ajbowler]

The overview API hits linescore.xml which has all of the useful probable starting pitcher info (ERA, names, player IDs, etc.)

Example: http://gd2.mlb.com/components/game/mlb/year_2018/month_02/day_25/gid_2018_02_25_chnmlb_sfnmlb_1/linescore.xml

This adds all of those attributes. Would appreciate a quick review and tag 😄 my LED board wants to scroll starting pitcher text across the screen and this file has the info readily available on at least the day before the game it seems.

[ajbowler]

Sorry the additional commit mess...still pretty nooby at Python

@panzarino so it looks like the unit tests are hitting the MLB servers directly. Since the probable starter attributes are time-dependent (they go away once the game starts) any test that grabs them would start failing after their "test date" has passed.

Also don't really see much I can improve upon for the code that's triggering the climate issue but I'd appreciate any feedback.

[panzarino]

@ajbowler looks good to me, for the tests that constantly change I just set it to test that the attributes are the correct type (basically just making sure they aren't null and the method actually works for the current data, ex. test roster). Can you please add tests for these new attributes and then I will merge.

[panzarino]

Please add test cases for new attributes

[ajbowler]

@panzarino code updated. The Travis build appears to be failing on some unrelated test

[panzarino]

@ajbowler not sure why that happened, restarted the build and it passed. Great work!