fixes #215 - add AMD support
always export  to globals, to prevent breaking existing implementations
fixes #257 - add retina support
Update removeMarkers, more efficient to clear all markers
FitZoom only use visible markers

Set the FitZoom method that it only get the visible markers.
Update README.md
Merge pull request #272 from iocron/patch-1

Update README.md
Merge pull request #265 from reinos/master

FitZoom only use visible markers
Merge pull request #256 from eighttrackmind/master

Add UMD support (AMD, CommonJS, browser globals), add retina support - fixes #215, fixes #257
Update version
Merge branch 'master' of github.com:HPNeo/gmaps
Update UMD template and README
Merge pull request #262 from lukluk/master

Update removeMarkers, more efficient to clear all markers
update copyright year
Merge pull request #286 from gdi2290/patch-1

update copyright year