PLINK-305 refactor credential handlers to work with custom identity model
Merge branch 'master' of github.com:picketlink/picketlink
added credential handler class diagram to docs
PL-190: clean up
Merge pull request #216 from anilsaldhana/master

PL-190: clean up
Merge branch 'master' of github.com:picketlink/picketlink
PLINK-305 allow specifying account types supported by the credential handler
rename credential handler property, updated docs
docs cleanup, start documenting custom credential handlers
[PLINK-305] - Merging changes.