ci : update + packages (#146)

* Add simple Debian package

* Update CI configuration

* Add cpack Deb package for libggwave-dev

* Add `make deb` top level target and CI job

* Ensure `make deb` packages are deterministic

Update CMakeLists.txt to make cpack generated Debian packages
deterministic build outputs by:
- Setting SOURCE_DATE_EPOCH to 0
- Executing `git log -1 --pretty=%ct` and storing the result in
  SOURCE_DATE_EPOCH, overriding 0
- Export SOURCE_DATE_EPOCH to the environment
- Explicitly prefix the execution of the cpack command in the custom
  target `deb_c_library` with SOURCE_DATE_EPOCH

Update `README.md-tmpl.md` and `README.md` to document new `make deb`
target.

The Makefile for the Python bindings already handle deterministic
building with the same strategy.

* libc6, not libc

bindings/python/debian/control

@@ -0,0 +1,40 @@
+Source: ggwave
+Section: python
+Priority: optional
+Maintainer: Georgi Gerganov <ggerganov@gmail.com>
+Build-Depends: debhelper-compat (= 13),
+               dh-python,
+               cython3,
+               python3-all-dev,
+               python3-setuptools,
+Standards-Version: 4.6.2.0
+Testsuite: autopkgtest-pkg-pybuild
+Homepage: https://github.com/ggerganov/ggwave
+Rules-Requires-Root: no
+
+Package: python3-ggwave
+Architecture: any
+Depends: ${misc:Depends}, ${python3:Depends}, ${shlibs:Depends},
+Description: Tiny data-over-sound library
+ Tiny data-over-sound library.
+ .
+ .
+  .. code:: python
+ .
+     # generate audio waveform for string "hello python"
+     waveform = ggwave.encode("hello python")
+ .
+     # decode audio waveform
+     text = ggwave.decode(instance, waveform)
+ .
+ .
+ --------
+ Features
+ --------
+ .
+  * Audible and ultrasound transmissions available
+  * Bandwidth of 8-16 bytes/s (depending on the transmission protocol)
+  * Robust FSK modulation
+  * Reed-Solomon based error correction
+ .
+ ------------