changed Table and DefaultClientAdaptorImpl classes -- refactoring
added new model DataType class. It represents types of columns like int, long, etc.
added new table model classes: {Item,Log}Table
added new request classes: Create{Item,Log}TableRequest
minor change of CreateTableRequest class
added new API in TreasureDataClient class: createItemTable method. It allows users to create new item tables.
changed test case of createTable
changed CHANGES.txt