v1.3.0

CHANGES:

• Implement affected_count for sqlite backend (GPR#46 jakob).
• Add method exec_with_affected_count to Caqti_connection_sig.S (GPR#45
  jakob).
• Add ?max_idle_size to pool creation functions.
• Dropped dependency on ppx_deriving due to issue with static compilation
  (GPR#50 Ulrik Strid).
• Pass through $<var>$ in query strings and deprecate $$.
• Log statements to be executed at debug level.
• Add COPYING.OCAML and fix license expression in opam files.
• Misc improvements to tests and documentation (GPR#51 Philippe Wang, GPR#54
  Reynir Björnsson, etc.).