Bump version to 1.15.0

[notmgsk]

Changelog

Features

• Use swap fidelity instead of gate time as a distance metric (@karalekas, @ecpeterson, Use swap fidelity instead of gate time as a distance metric #331).
• Support for defining gates as pauli-sums, and parametric compilation thereof (@ecpeterson, Feature: "DEFEXPI" #498).
• Use alternative CS decomposition when it is missing from LAPACK (@jmbr, Use alternative CS decomposition when it is missing from LAPACK #485).
• Parse OpenQASM (@notmgsk, Parse OpenQASM #495).

Bugfixes

Improvements

• Write unit test for EXP-PAULI (@jmbr, Write unit test for EXP-PAULI. #496).
• Add DIRECTION as frame attribute (@kilimanjaro, Add DIRECTION as frame attribute #499).
• Use SAFELY-PARSE-QUIL on external input (@notmgsk, Use SAFELY-PARSE-QUIL on external input #500).