0.5.2: More primitive operations

Highlights from README:

• Supports a lot of primitive operations (including ternary ops), and ternary tensor operations.
• %cd and %op support both curried and uncurried operator application syntax.
• More flexible gradient construction via the %cd syntax (better projections inference).
• Works on Native Windows with the C compiler backend (but CUDA backend blocked by cudajit still).

Details from the changelog:

Added

• Lots of new primitive ops:
  • Unary: Satur01 | Exp | Log | Exp2 | Log2 | Sin | Cos | Sqrt | Recip | Recip_sqrt | Neg | Tanh_approx | Not
  • Binary: Satur01_gate | Max | Min | Mod | Cmplt | Cmpeq | Cmpne
  • Ternary: Where | FMA (non-accumulating)
• Ternary tensor operations.
  • A differentiable where operation.
• More flexible gradient construction via the %cd syntax (better projections inference).
• CC backend piggy-backing on OCaml's C compiler (consistent across OSes).

Changed

• Updated to printbox 0.12, with upstreamed graphing.
• -pthread -> -lpthread in c_library_flags in dune files.
• Removed Numpy support for easier compatibility on native Windows.
• Unary (primitive) ops and relu are now named, not operator syntax.
• Refactored %cd parsing of primitive ops.
• %cd and %op support both curried and uncurried operator application syntax.
• Updated to ppx_minidebug 2.2.0 with support for cross-run diffing.

Fixed

• Numbers text rendering (consistent across OSes).
• Moved closing row variables to stage 3, because stage 2 may need to process inequalities generating more LUBs.
• Don't unnecessarily prevent bytecode-only build targets.