Standardized CPTFloat() usage with negative numbers to put the negative sign inside the parentheses.
Added a check for invalid view points in CPTXYAxis to prevent crashing. Fixed issue 575.
Marked some private animation constants as static. Fixed issue 576.
Merged the default branch into the release-2.0 branch.
Changed the return type of all initialization methods to "instancetype" for better compile-time type checking.