r2

Changes:

pbss:

• buffer and related types and functions, to eliminate one pass of memset in serialization, giving a significant speedup
• optimistic parsing on large custom structs, performs good when input exactly matches the current schema definition but is slower when they do not match

pbsf:

• the library no longer exports symbols of its internal functions
• allows appending to existing sequential file

general and pbsu:

• the whole library no longer requires -fno-strict-aliasing; this comes with an ABI-breaking change in the implementation of optional