setup: access version w/o __init__ to avoid circular imports (#56)

+ setup.cfg: setup the version number via `version.release_version`, instead of going through `__init__`, to avoid the circular imports that causes the pip install "ModuleNotFoundError"
+ setup.cfg: add `install_requires` and remove `[opptions.package_data]` to be consistent with compass
+ __inti__.py: use absolute module import, to be consistent with the good style from pyresample module
+ version.py: remove the duplicated `__version__` variable.

setup.cfg

@@ -1,7 +1,7 @@
 [metadata]
 name = s1reader
-version = attr: s1reader.__version__
-description = A Sentinel1 metadata reader
+version = attr: s1reader.version.release_version
+description = A Sentinel-1 reader for ISCE3
 long_description = file: README.md
 long_description_content_type = text/markdown
 url = https://github.com/opera-adt/s1-reader
@@ -16,10 +16,12 @@ classifiers =
 package_dir =
     = src
 packages = find:
-python_requires = >=3.9
 include_package_data = True
+python_requires = >=3.9
+install_requires =
+    setuptools
+    importlib_resources
 
 [options.packages.find]
 where = src
-[options.package_data]
 

src/s1reader/__init__.py

@@ -1,7 +1,7 @@
 # version info
-from .version import release_version as __version__
+from s1reader.version import release_version as __version__
 
 # top-level functions to be easily used
-from .s1_burst_slc import Sentinel1BurstSlc
-from .s1_reader import load_bursts
-from .s1_orbit import get_orbit_file_from_dir
+from s1reader.s1_burst_slc import Sentinel1BurstSlc
+from s1reader.s1_reader import load_bursts
+from s1reader.s1_orbit import get_orbit_file_from_dir

src/s1reader/version.py

@@ -14,5 +14,3 @@
 release_version = release_history[0].version
 release_date = release_history[0].date
 
-# variable
-__version__ = release_version