Rashdf

Features
* **2D Mesh Summary Output Data**: ability to export mesh Summary Output data from Plan HDF files. (e.g., Maximum Water Surface, Maximum Face Velocity, Cell Maximum Water Surface Error, etc.)
* Summary output data can be exported to pandas `DataFrame` objects via methods such as: `mesh_max_ws`, `mesh_max_face_v`, `mesh_max_ws_err`, etc.
* The methods `mesh_cell_points`, `mesh_cell_polygons`, `mesh_cell_faces` now include available summary output columns in the GeoDataFrame by default when an HDF file is opened with `RasPlanHdf`.
* **2D Mesh Timeseries output**: ability to export mesh time series output data as xarray `DataArray` / `Dataset` objects. New `RasPlanHdf` methods include:
* `mesh_timeseries_output`: export a specific timeseries output as a `DataArray` object
* `mesh_timeseries_output_cells`: export cell-based timeseries output data as a `Dataset`
* `mesh_timeseries_output_faces`: export face-based timeseries output data as a `Dataset`

Fixes an issue where `rashdf` was unable to export mesh cell polygons from certain HEC-RAS HDF files due to topology problems. HEC-RAS allows mesh cells with overlapping cell face lines. `rashdf` now allows this as well.

See issue: 31

Fixes an issue with `rashdf`'s datetime parsing functionality to handle the way RAS represents midnight in string format as `24:00:00` rather than `00:00:00` of the next day. For example, a RAS datetime string of `31Dec2023 24:00:00` should parse to a Python datetime of `datetime(year=2024, month=1, day=1, hour=0, minute=0, second=0)`, i.e., `00:00:00` on January 1.

Features
* `rashdf` command-line interface
* `structures` method implemented

Fixes an issue with `rashdf.utils.convert_ras_hdf_string`. The already-existing function `rashdf.utils.parse_duration` wasn't getting used as intended to parse RAS HDF time duration strings. This update ensures that RAS HDF attribute string values in the format `HH:MM:SS` are converted to `datetime.timedelta` objects.

Features
* Initial classes for `RasHdf`, `RasGeomHdf`, `RasPlanHdf` as subclasses of `h5py.File`
* Methods implemented:
* `projection`: return the projection as a pyproj `CRS` object
* `mesh_area_names`: return the list of 2D mesh area names
* `RasGeomHdf` methods returning `GeoDataFrame` objects:
* `mesh_areas`: 2D flow area perimeter polygons
* `mesh_cell_polygons`: 2D flow area cells as polygons
* `mesh_cell_points`: 2D flow area cell centers
* `mesh_cell_faces`: 2D flow area cell faces as lines
* `bc_lines`: 2D boundary condition lines
* `breaklines`
* `refinement_regions`
* Methods to return dictionaries of attributes (i.e., metadata) for certain HDF groups:
* `RasGeomHdf`:
* `get_geom_attrs`
* `get_geom_structures_attrs`
* `get_geom_2d_flow_area_attrs`
* `RasPlanHdf`:
* `get_plan_info_attrs`
* `get_plan_param_attrs`
* `get_meteorology_precip_attrs`
* `get_results_unsteady_attrs`
* `get_results_unsteady_summary_attrs`
* `get_results_volume_accounting_attrs`