Bump BOOST_GIL_VERSION for Boost 1.72?

From: Mateusz Loskot (mateusz_at_[hidden])
Date: 2019-11-06 17:55:56

Hi,

Currently, the internal version is 22 (aka 2.2) set for Boost 1.68.
Given the extensive additions to public API during GSoC,
shall we bump the number?

I think it is right to make it 3.0.

Objections? Opinions?

[1] https://github.com/boostorg/gil/blob/3b8398f17cc91ae1501be9d1d8c204f5cb241ece/include/boost/gil/version.hpp

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net