Merge branch 'develop'

Merge pull request flame-engine#317 from flame-engine/develop

0.20.1 RC

Merge pull request flame-engine#308 from flame-engine/develop

0.20.0 RC

fixing changelog

Merge pull request flame-engine#271 from flame-engine/develop

0.19.0 RC

Merge pull request flame-engine#263 from flame-engine/develop

0.18.3 RC

Merge pull request flame-engine#244 from flame-engine/develop

0.18.2 RC

Merge pull request flame-engine#217 from flame-engine/develop

0.18.1 RC

Merge pull request flame-engine#214 from flame-engine/develop

0.18.0 RC

Fixing box2d_flame dependency