Fix tables in docstrings

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/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages/fasttrips/Util.py:docstring of fasttrips.Util.calculate_pathweight_costs:12: WARNING: Malformed table.
Text in column margin in table line 7.
==================  ===============  =====================================================================================================
column name          column type     description
==================  ===============  =====================================================================================================
`var_value`                 float64  The value to weight
`growth_type`                   str  ['constant', 'exponential', 'logarithmic', 'logistic']
`growth_log_base`           float64  [logarithmic only] log base for logarithmic base value
`growth_logistic_max`       float64  [logistic only] Maximum assymtotic value for logistic curve
`growth_logistic_mid`       float64  [logistic only] X-Axis location of the midpoint of the curve
==================  ===============  =====================================================================================================

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/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages/fasttrips/Route.py:docstring of fasttrips.Route.fare_rules_df:12: WARNING: Malformed table.
Text in column margin in table line 10.
===================  =====================================================================================================================================
 Column name         Column Description
===================  =====================================================================================================================================
`fare_id`            GTFS fare_id (See `fare_rules`_)
`fare_id_num`        Numbered fare_id
`route_id`           (optional) Route(s) associated with this fare ID. (See `fare_rules`_)
`origin_id`          (optional) Origin fare zone ID(s) for fare ID. (See `fare_rules`_)
`origin_id_num`      (optional) Origin fare zone number for fare ID.
`destination_id`     (optional) Destination fare zone ID(s) for fare ID. (See `fare_rules`_)
`destination_id_num` (optional) Destination fare zone number for fare ID.
`contains_id`        (optional) Contains fare zone ID(s) for fare ID. (See `fare_rules`_)
`fare_period`        GTFS-plus fare_period (See `fare_periods_ft`_)
`start_time`         Fare class start time (See `fare_rules_ft`_)
`end_time`           Fare class end time (See `fare_rules_ft`_)
`currency_type`      Currency of fare class or id (See `fare_attributes`_ or `fare_attributes_ft`_)
`price`              Price of fare class or id (See `fare_attributes`_ or `fare_attributes_ft`_)
`payment_method`     When the fare must be paid (See `fare_attributes`_ or `fare_attributes_ft`_)
`transfers`          Number of transfers permiited on this fare (See `fare_attributes`_ or `fare_attributes_ft`_)
`transfer_duration`  (optional) Integer length of time in seconds before transfer expires (See `fare_attributes`_ or `fare_attributes_ft`_)
===================  =====================================================================================================================================