New option "keepAspectRatio"

[rastafan]

This PR adds a new option "keepAspectRatio", to manage the ability to change the cropped image's aspect ratio.

OLD BEHAVIOUR:
-Android : Aspect ratio il locked to 1:1 if targetWidth and targetHeight are equal or if both are -1, else it is not locked;
-iOS : Aspect ratio is always locked to the one specified by targetWidth:targetHeight

NEW BEHAVIOUR:
-Android AND iOS : If keepAspectRatio!=0, aspect ratio is locked to targetWidth:targetHeight (or 1:1 if they are equal). If KeepAspectRatio==0, the ratio is unlocked and can be modified as desired;

Also, on iOS, it now respects the size specified with targetWidth and targetHeight, instead of starting always with a square cropped image. If -1 is specified on one of the two dimension, that dimension is replaced by the picture corrisponding dimension.

This may be resolving #49, #50, #75 and #76

[rjurado01]

I have check it and it works, please merge !!

Thanks @rastafan

[mbenfriha]

how to use "keepAspectRatio" in ionic ?

[rjurado01]

@mbenfriha

plugins.crop(function success () {
}, function fail () {
}, '/path/to/image', {keepAspectRatio: 0})

See Readme: https://github.com/jeduan/cordova-plugin-crop/pull/77/files