Fix Xcode 8.3 compiler warnings

[krbarnes]

Xcode 8.3 introduces a bunch of new compiler warnings. This PR fixes them.

• Replace M_PI_2 with Double.pi / 2
• Replace M_PI with Double.pi
• Replace DBL_MAX with Double.greatestFiniteMagnitude
• Replace DBL_EPSILON with Double.ulpOfOne

[codecov-io]

Codecov Report

Merging #2279 into master will increase coverage by 0.14%.
The diff coverage is 33.96%.

@@            Coverage Diff             @@
##           master    #2279      +/-   ##
==========================================
+ Coverage   18.44%   18.58%   +0.14%     
==========================================
  Files         124      124              
  Lines       14619    14508     -111     
==========================================
  Hits         2696     2696              
+ Misses      11923    11812     -111

Impacted Files	Coverage Δ
Source/Charts/Animation/ChartAnimationEasing.swift	0% <ø> (ø)	⬆️
...Data/Implementations/Standard/ChartDataEntry.swift	6.45% <0%> (ø)	⬆️
Source/ChartsRealm/Data/RealmBaseDataSet.swift	0% <0%> (ø)	⬆️
Source/Charts/Highlight/RadarHighlighter.swift	0% <0%> (ø)	⬆️
Source/ChartsRealm/Data/RealmBubbleDataSet.swift	0% <0%> (ø)	⬆️
Source/ChartsRealm/Data/RealmBarDataSet.swift	0% <0%> (ø)	⬆️
.../Implementations/Standard/ChartDataEntryBase.swift	8.33% <0%> (ø)	⬆️
...a/Implementations/Standard/CombinedChartData.swift	0% <0%> (ø)	⬆️
Source/Charts/Renderers/PieChartRenderer.swift	0% <0%> (ø)	⬆️
Source/ChartsRealm/Data/RealmCandleDataSet.swift	0% <0%> (ø)	⬆️
... and 7 more

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[liuxuan30]

It has merged already. update your repo.
BTW, I don't see it complains about M_PI and EPSILON, but greatestFiniteMagnitude has been updated.

[liuxuan30]

oops, sorry, I missed yo said Xcode 8.3 errors.

[liuxuan30]

should be fine to merge.