Add option to hide keys in log and print sha256(key) instead

[moticless]

• Extend librdb-api.h with RDB_hideKeysInLog(RdbParser *p) to hide keys in logs during errors by printing the first 8 hex digits of SHA256(key).
• Rename ./src/ext/common.h to “/src/ext/extCommon.h
• Avoid printing twice the reported error message. (The first time occurs when calling to RDB_reportError() and the second time at the end of parserMainLoop(), by calling printParserState()).
• On error, add to printParserState() also the value of bytesRead of the parser.
• On elementEndKey(), set ...dataType = RDB_DATA_TYPE_MAX; for completeness.

[tezc]

glanced over changes quickly, it looks good to me.