state(): uCDB state. open(): hash tab pos can't be 0. More tests

uCDB constructor, const class members moved to class decl

findKey(): reuse last accessed hash table info if possible

examples: serial baud - 115200

Macro RETURN(): tracing errors

recordsNumber(): state check fix.

API: valueAvailable() - the number of (value) bytes available for rea…

…ding, recordsNumber() - total number of records in CDB

Relax FILE_ERROR handling. Benchmark example

API changes: COMPARE_HASH_ONLY removed