Query article by zbl id

Closes ptf-site-gdml#1 (closed)

• Adds one route : api-article-xml/<path:id_type>/<path:id_value>

Valid id_type are :

• doi
• pid
• zblid

Examples :

http://geodesic-test.mathdoc.fr/api-article-xml/zblid/06701808/

http://geodesic-test.mathdoc.fr/api-article-xml/doi/10.5802/ambp.82/

http://geodesic-test.mathdoc.fr/api-article-xml/pid/MABA_2013_27_1-2_a0/