Bbc1

* Fix problem regarding new version of gevent
* Fix codes in deprecated usage

* Support BBcAssetRaw and BBcAssetHash defined in py-bbclib v1.5 or later
* bug fix

* Decouple bbclib from bbc1/core
* import py-bbclib
* Skip signature verification if no public key included in BBcSignature

* Support timestamp-based transaction search
* search_transaction_with_condition() method in bbc_app.py is upgraded to include start\_from and until params
* DB meta table (asset_info_table) is upgraded (timestamp column is added)
* Migration tool is implemented (utils/db_migration_tool.py)
* Add a new step-by-step style example in github (examples/starter)
* Bug fixes

* Re-design and refactor bbclib.py
* serializing transaction object consists of packing object into binary and serializing it into wire format. (new format types are 0x0000 and 0x0010)

* Fix bug on installation with pip in Linux environment