New syntax def

[guillermooo]

This PR adds a syntax def for PS in the new .sublime-syntax format.

Advantages:

• LL(1) parsing
• tests for syntax definition

---

Currently working on

• [x] embedded docs
  • [x] section titles
  • [x] title arguments
• [x] script blocks
• [ ] params()
• [x] variable names
  • [x] short ($Foo)
  • [x] long (${weird name})
  • [x] scoped ($script:wtf)
• [x] strings
  • [x] single quoted
  • [x] double quoted
  • [x] @'
  • [x] @"
  • [x] string interpolation simple
  • [x] string interpolation subexpr

    Maybe later / You take it

• [ ] foo

[guillermooo]

BTW, I'm making up the scope names as I go. If anyone has better ideas, please chip in!