Merge pull request #554 from emmanuel-keller/master

MoreLikeThis query sorted in score descending order.
Merge pull request #557 from emmanuel-keller/master

MoreLikeThis API returns query string
Merge pull request #560 from emmanuel-keller/master

Error message on invalid OPENSEARCHSERVER_DATA environment variable
Merge pull request #564 from emmanuel-keller/master

Implements issue #561
Merge pull request #569 from emmanuel-keller/master

Testing framework
Merge pull request #572 from emmanuel-keller/master

Add additionnals libs for the external parser
Update get%7Cretrieving_a_more-like-this_template%7C2.md

Minuscule fixes.
Update list%7Cget_the_list_of_the_more-like-this_templates%7C1.md

Minuscule changes.
Merge pull request #574 from emmanuel-keller/master

Support of specific classpath for external parser