Fix representation of negative values in Y axis
Merge branch 'travis-fix' into correct-min-values-representation
resolve merge conflict with #79 (it's a subset of these pull-request)
Merge branch 'code-improvements'
fix issue #80
Merge branch 'travis-fix' into fix-80
Merge pull request #79 from ben181231/master

Fix several UI bug when displaying data with negative numbers
Merge pull request #83 from skywinder/correct-min-values-representation

Fix representation of negative values in Y axis
Merge pull request #85 from skywinder/improve-Example

Fix wrong presentation of years in code exmple + auto-update graph by clicking on segment controll
Merge pull request #86 from skywinder/fix-80

fix issue #80
Changed behavior of property 'enableXAxisLabel'

- Changed documentation for ‘enableXAxisLabel’
- ‘enableXAxisLabel’ now defaults to YES. This way implementing the
method ‘labelOnXAxisForIndex’ is enough to display the labels.
‘enableXAxisLabel’ becomes an option.
Split enableReferenceAxisLines into two properties

Allow individual specifying of just X, Y or both reference lines
Merge pull request #87 from gavinbunney/master

Split enableReferenceAxisLines into two properties
Added colorReferenceLines property to alter reference line stroke color
Altered draw order of graph to ensure reference lines are behind the graph line
Merge pull request #88 from gavinbunney/master

Reference line color & draw order
Merge remote-tracking branch 'origin'
Rename enums to simplify code review.
Merge branch 'code-improvements'