v0.18.8

DistributedFactorGraphs v0.18.8

Diff since v0.18.7

Merged pull requests:

• Better error message on getSolverData (#903) (@dehann)
• bug fix on mergeDataEntries (#909) (@dehann)
• kwarg to skip version checking on unpackVariable for performance (#910) (@Affie)
• enhancements for blob caching (#911) (@dehann)
• v0.18.8-rc1 (#912) (@dehann)