1. database connection handled. setup function and ConnectionPool class written
2. exception classes extended from base exception class
Merge remote-tracking branch 'origin/connection'

Conflicts:
	test_pycql.py
== Merged and updated ==
    + rewrite the object mapper
Rearranged and fixed the method calling hierarchy
@object_mapper
    + dynamic method for cql types
@object_mapper
    + docstings
    + cql_type specific methods to set column definition easily
    + set, list and map support

@test_object_mapper
    + test_table [all tests are passed]
@object_mapper
    + set primary key support

@test_object_mapper
    + primary key [all tests are passed]