Updating to capnproto v0.8.0

- Includes some test stabilization
- Fixes manylinux2010 build issues (linker flag order due to old gcc)
- More rigorous python setup.py clean
- Requires capnproto v0.8.0 or greater
- Including system libcapnp include path for import (e.g. import
  stream_capnp)
- Bundle libcapnp .capnp files when not using system libcapnp
- Removing more distutils usage. Now using pkg-config to determine the
  system version of libcapnp (mainly for Linux, but should work on macOS
  with brew)
- Removed dead code

Resolves issues #215 #216 #217
Lots of fixes for Issue #218 (all sorts of retry methods needed for
GitHub Actions)

README.md

@@ -20,7 +20,7 @@
   - ninja (macOS + Linux)
   - Visual Studio 2017+
 
-* capnproto-0.7.0
+* capnproto-0.8.0
   - Not necessary if using bundled capnproto
 
 32-bit Linux requires that capnproto be compiled with `-fPIC`. This is usually set correctly unless you are compiling canproto yourself. This is also called `-DCMAKE_POSITION_INDEPENDENT_CODE=1` for cmake.
@@ -55,6 +55,18 @@ To force bundled python:
 pip install --install-option "--force-bundled-libcapnp" .
 ```
 
+Slightly more prompt error messages using distutils rather than pip.
+
+```bash
+python setup.py install --force-bundled-libcapnp
+```
+
+The bundling system isn't that smart so it might be necessary to clean up the bundled build when changing versions:
+
+```bash
+python setup.py clean
+```
+
 
 ## Python Versions