Update installation instructions to use conda and github

[djhoese]

The installation instructions all used google code which isn't used any more. They also had a lot of instructions for installing aggdraw and other dependencies which shouldn't be needed any more.

[coveralls]

Pull Request Test Coverage Report for Build 24

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 44.393%

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Totals
Change from base Build 30:	0.0%
Covered Lines:	190
Relevant Lines:	428

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💛 - Coveralls

[codecov]

Codecov Report

Merging #13 into master will not change coverage by %.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #13   +/-   ##
=======================================
  Coverage   44.26%   44.26%           
=======================================
  Files           4        4           
  Lines         427      427           
=======================================
  Hits          189      189           
  Misses        238      238           

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