+ identify SLC stack as "FILE_TYPE==timeseries" and "DATA_TYPE==complex(64/128)"

+ stack.timeseries.open): change CENTER_LINE_UTC from required to optional as SLC stack might not have it

+ readfile.read_attribute(): check SLC stack and reset UNIT to 1

+ coord.geo2radar(): ensure the consistency between point longitude and source file, regardless of the source file convention in (-180, 180] or [0, 360) conventions. For geocoded files only.

+ plot:
   - auto_colormap_name(): use gray as default cmap for slc stack
   - auto_adjust_xaxis_date(): smart every_year/month for extra long time series, e.g. GRACE products.

+ view:
   - read_data4figure(): take abs() if data type is complex
   - move code to form check_map_projection() for easy re-use, e.g. in tsview.py

+ tsview:
   - pass `disp_unit` directly for the model estimation result display, for more simple and robust performance against input files that are not in the unit of meters, e.g. giant product or GRACE products.
   - grab WAVELENGTH if and only if wrap-range is 2 pi. This allows applying --wrap-range option to files w/o WAVELENGTH attributes, e.g. the GRACE products.
   - support cartopy map projection and its related features, e.g. --coastline, via view.check_map_projection()
   - take abs() if data is complex
   - bugfix for --flip-lr/ud options

+ rename `legacy/load_hdf5.py` to `legacy/load2hdf5.py`
+ refactor to be more flexible on the input/output file structure
+ add --sub-x/y
+ add --meta to add custom metadata
+ support --dname timeseries with "date" dataset added automatically
+ add DATA_TYPE_STR2OBJ to support most common numpy data types
+ check if the output file exists with --force option

+ add a new standard metadata: NO_DATA_VALUE

+ readfile.py:
   - read_attribute(): grab NO_DATA_VALUE with 'none' as default
   - add get_no_data_value() to get the value of the input file
   - add SPECIAL_STR2NUM() to facilitate no_data_value handling
   - read_isce_xml() / read_gdal_vrt(): grab NoDataValue if exists.

+ view.py: mask out pixels with no_data_value for single subplot

+ tests/config/*.txt: speedup testing by decrease plot.maxMemory to 2GB to use more parallel processes for plotting