* minor modifications of performance tests
* minor changes to ecoxipy.deorators
* fixed document encoding bug in ecoxipy.string_output
* updated performance tests
* added HTML5_ELEMENT_LIST doc in ecoxipy.decorators
* minor modification to documentation index page
* renamed ecoxipy.decorators.HTML5_ELEMENT_LIST to HTML5_ELEMENT_NAMES and made it an sets.ImmutableSet instead of tuple
* updated doc of ecoxipy.decorators.HTML5_ELEMENT_NAMES