added exceptions handling for importing to be possible over existing labels
changed avatar size and added extra footer infos
tweak issue object to contain extra fields used by the template file
new comment template file using mustache like for issues posts
calling pystache to use comment template when importing comments
added missing extra fields to object passed to pystache comment template
fixed not indexing github issue objects by bitbucket id
use bitbucket username when no convertible github user found in config
fixed not calling the correct PyGithub function to create issue comments
force all script strings to be encoded as unicode by default