Use canonical property names in paths

[mathiasbynens]

E.g. instead of /categories/ use General_Category.

• bidi-classes → Bidi_Class
• bidi-mirroring → Bidi_Mirroring_Glyph
• blocks → Block
• case-folding → Case_Folding
• categories → General_Category
• script-extensions → Script_Extensions
• scripts → Script
• properties → Binary_Property (this is a made-up name) or move to top-level?
• bidi-brackets → needs to be split up in Bidi_Paired_Bracket (currently unused so could be dropped) and Bidi_Paired_Bracket_Type