Update version to 1.3.1

Preparing release 1.3 (fraunhoferhhi#117)

* Merged changes for 1.3: string API, 1pRC with preanalysis, tile parallelism, proper FPS signaling, low rate QPA improvements, cleanups

* update VTM reference

Merge pull request fraunhoferhhi#100 from adamjw24/develop_1.2

Changes for 1.2.0 (5% BD-rate improvement for faster)

Merge pull request fraunhoferhhi#78 from adamjw24/develop_v1.1

Version 1.1

Merge pull request fraunhoferhhi#64 from adamjw24/develop_100

version bump

Merge pull request fraunhoferhhi#30 from adamjw24/develop_v0.3.1.0

Merged changes for v0.3.1.0

Merge pull request fraunhoferhhi#21 from adamjw24/develop_v0.3

Merged changes for v0.3

Merge pull request fraunhoferhhi#14 from fraunhoferhhi/develop_v0.2.1.0

develop v0.2.1.0

Merge pull request fraunhoferhhi#11 from adamjw24/develop_v0.2.0.0

Develop 0.2.0.0

Merge pull request fraunhoferhhi#7 from adamjw24/develop_fixSimpleApp…

…Simd

Fix SIMD activation in simple encoder