Add built-in chrome service capabilities

[iiLaurens]

I propose a new version in which PyChrome automatically initiates a chrome service. This takes the effort away from the end user to manually start the Chrome application. The chrome service will simply launch a chrome process on the background and automatically connects. The PyChrome user can simply control this chrome instance as usual.

By default, a headless chrome instance will be started. At every start, a new chrome user is created in order to start with a clean slate and make testing reproducible as cookies are not stored permanently.

I have added context managers that gracefully cleans up the chrome service if the Browser instance is removed. It is also possible to start a Browser using a with statement. I also added a couple of tests and changed the existing tests to use the automatic chrome service.

[codecov[bot]]

Codecov Report

Merging #27 into master will decrease coverage by 3.62%. The diff coverage is 86.52%.

@@            Coverage Diff             @@
##           master      #27      +/-   ##
==========================================
- Coverage   93.36%   89.74%   -3.63%     
==========================================
  Files           4        6       +2     
  Lines         211      351     +140     
  Branches       21       36      +15     
==========================================
+ Hits          197      315     +118     
- Misses          7       19      +12     
- Partials        7       17      +10

Impacted Files	Coverage Δ
pychrome/browser.py	90.19% <81.81%> (-7.37%)	:arrow_down:
pychrome/tempdir.py	84.61% <84.61%> (ø)
pychrome/service.py	87.17% <87.17%> (ø)
pychrome/tab.py	90.78% <0%> (-0.66%)	:arrow_down:

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