Tidy documentation naming

[chrismclarke]

During the course of development we jumped back and forth on naming (documentation -> docs -> tutorials). As Dave and Mattia seem fixed on documentation.preciousplastic.com I think it makes most sense to go back to documentation (not docs), and rename things accordingly.

@BenGamma, let me know if you want me to implement this or if you want to yourself.

child of #3

[chrismclarke]

now how-to's, needs to be updated

[chrismclarke]

done by @BenGamma , closing