v0.9.0

DynamicPPL v0.9.0

Diff since v0.8.2

Closed issues:

• Crease a dev branch for breaking changes (#73)
• Respect user-provided function signatures (#106)

Merged pull requests:

• Fix prob macros (#147) (@devmotion)
• Try to avoid pmap test issues (#157) (@devmotion)
• Merge changes in dev branch into master (#158) (@yebai)