Add summarize framework
Read model types from M_c in summarize_table, summarize continuous vars
Using describe() on all columns now, added function to calculate most frequent values of each column
Added tests for summarize
Not calculating row_id summary stats, dynamic output of index labels in get_column_freqs
Cleaned up conversion from DataFrame back to list of lists, handled columns with more than 5 unique values
Added empirical probabilities of most frequent values, added row_index to output table
Drop unnecessary rows from summary and allow duplicate column names in output
Only removes top and freq rows when a discrete column is included
Test summarize with functions, and cases where all variables are the same type
Drop row_index from summarize output
Summarize doesn't do anything if len(data) == 0
Fixed error when constructing a DataFrame from 0 rows
Needed to update argument to pandas.DataFrame in construct_pandas_df
Only remove row_id column if it's found
Reorder output rows to count, unique, std, min, 25/50/75%, max, modes, prob_modes, where calculated
Update parser test for summarize
Merge branch 'master' into summarize

Conflicts:
	bayesdb/engine.py
	bayesdb/parser.py
	bayesdb/tests/test_client.py
	bayesdb/tests/test_parser.py
Fix summarize for old pandas versions
Fix tests