Use grunt options for task configuration

See grunt-wiredep #92 for more information. This will be a breaking
change for current configurations. To upgrade the configuration: wrap
all options for the wiredep task in Gruntfile.js (except for the src
option) in an options object.
Backward compatibility for the task configuration

Extend the options object with the properties that are specified in the
old way (through the this.data object) to provide backward
compatibility.
Updated the documentation for the new configuration
Minor style fix for the documentation
Merge pull request #94 from pacbeckh/master

Use grunt options for task configuration