* adding file position index data accessable to the chain, and allowing for storage of such within db
* missing file
* restart files at last recorded position in stored file metadata
* just use tip to store last pmmr index information
* error handling
* test fix
* beginning to remove sum
* continuing to remove sumtree sums
* finished removing sums from pmmr core
* renamed sumtree files, and completed changes+test updates in core and store
* updating grin/chain to include removelogs
* integration of flatfile structure, changes to chain/sumtree to start using them
* tests on chain, core and store passing
* cleaning up api and tests
* formatting
* flatfiles stored as part of PMMR backend instead
* all compiling and tests running
* documentation
* added remove + pruning to flatfiles
* remove unneeded enum
* adding sumtree root struct
