Added mexican.bib
Added some new books from bne.es, updated classification
Added some N. Malpied works
Added license.txt
Added some new books, modified data for monsort_1769
Added constraint check for url presence in thesises
Fixed Boiseul book, added 16th century basse bance book
Added some books from Greg Lindahl bibliography
Added one more ballet book, fixed some mistakes
Implemented polish language support (not working yet)
Added american lady's book
Sorted entries in polish.bib
Fixed font encoding error in polish language support
Added german Arbeau translation
Added spanish small sequence dance
Fixed errors
Added Arbeau translation commentator
Updated Livio Lupi books description
Added more itatian libri di gagliarda
Added Prospero Luti book transcription