Support gesture and direct function

1. Android and iOS gesture support.
2. Enable calling function on chart instance directly.

Add StyledCenterText support for PieChart

Add StyledCenterText support for PieChart

Bug fix and new features

Compatible to RN4.7+.
Add viewport support.
Add rotationAngle for Pie/Radar Chart.
Add digit format in marker.
Add date formatter.

fix config for bar chat

v0.2.10

update package.json

fix marker for stacked bar

v0.2.9

update package.json

fix pie entryLabelTextSize&entryLabelColor, add valueTextSize&valueTextColor

v0.2.8

update package.json

fix HorizontalBar

v0.2.7

update package.json

update SwiftyJSON to fixed version '3.1.4'

v0.2.6

update README

add horizontal bar chart support

several bug fix.
support horizontal bar chart

value label support valueTextSize and valueFormatter.

fix issue #12