Biblio update and Xper3 tutorial

Hi everyone!

We hope that you are all safe and sound. The current Covid-19 lockdown did not help to work on IDmyBee. It especially slowed down the development of ID tools related to the Melittidae (no access to the collections for pictures and coding), but we managed to work on the website.
First, we owe a big thank to Rafael Carbonell Font. Thanks to his contribution, we expanded our bibliography (now more than 150 references) and we added links to about a hundred of online pdfs! If you don't know what to do during this lockdown, you can read them here.
A first (and short) list of online resources was also added here, and in the different genera pages when relevant. We hope to expand this list soon, so don't hesitate to contact us to suggest more resources.
Finally, we made a couple of snapshots to help users with Xper3. Although Xper3 is pretty intuitive, we invite you to check this page here, as well as the original website of the software (Xper3.fr and the associated wiki).
We hope that these changes will help you to use IDmyBee for your studies.

Adrien, for the team of IDmyBee