use the posix-compliant __linux__ preprocessor symbol

ofxsProperty: workaround for a clang>=14 bug with -O2

Bug observed on OSX 10.9 (causes a segfault)

Add BSD license

The OFX standard is released under a BSD license; this commit
adds a standard LICENSE.md file detailing that license.
Fixes AcademySoftwareFoundation#79.

Update .travis.yml.disabled

plugins: experimental support for macOS Universal arm64/x86_64

expat -> 2.3.0 (step 2)

Merge branch 'master' of https://github.com/NatronGitHub/openfx

fix kOfxParamPropChoiceOptionName constant

Revert "Merge branch 'distortion'"

This reverts commit 5fd6a5c, reversing
changes made to 55f4281.

Re-tagging release 1.4.