Implement blackbox in Golang (#250)

* Initial release

docs/compatibility.md

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+Compatibility
+=============
+
+# Compatibility with Blackbox v1
+
+The command names all changed from v1 to v2.  The `binv2` directory
+includes shell scripts that provide full backwards compatibility.
+
+# Supported Architectures
+
+Blackbox supports a plug-in archtecture to easily support multiple VCS
+system.  Current support is for:
+
+## Supported VCS/DVCS systems
+
+* git
+* "none" (repo-less use is supported)
+* WOULD LOVE VOLUNTEERS TO HELP ADD SUPPORT FOR: hg, svn, p4
+
+## Supported GPG versions
+
+* Git 1.x and 2.0
+* Git 2.2 and higher
+* WOULD LOVE VOLUNTEERS TO HELP ADD SUPPORT FOR:
+  golang.org/x/crypto/openpgp (this would make the code have no
+  external dependencies)
+
+## Supported Operating systems
+
+Blackbox should work on any Linux system with GnuPG installed.
+Blackbox simply looks for `gpg` in `$PATH`.
+
+Windows: It should work (but has not been extensively tested) on
+Windows WSL2.
+
+# Automated testing
+
+While many combinations work, we do automated tests
+on these combinations.  If any of these fail it blocks the release:
+
+* macOS: GnuPG 2.2 executables from https://gpgtools.org/
+* CentOS: GnuPG 2.0.x executables from the "base" or "updates" repo.
+
+Windows native: VOLUNTEER NEEDED to make a native Windows version
+(should be rather simple as Go does most of the work)
+
+NOTE: Version 1 worked on CentOS/RedHat, macOS, Gygwin, WinGW, NetBSD,
+and SmartOS.  Hopefully we can achieve that broad level of support in
+the future.  Any system that is supported by the Go language and
+has GuPG 2.0.x or higher binaries available should be easy to achieve.
+We'd also like to have automated testing for the same.
+
+# Windows Support
+
+BlackBox assumes that `blackbox-admins.txt` and `blackbox-files.txt` will have
+LF line endings. Windows users should be careful to configure Git or other systems
+to not convert or "fix" those files.
+
+If you use Git, add the following lines to your `.gitattributes` file:
+
+    **/blackbox-admins.txt text eol=lf
+    **/blackbox-files.txt text eol=lf
+
+The `blackbox init` (and newer versions of `blackbox_initialize`)
+will create an appropriate `.gitattributes` file for you.
+
+# Cygwin
+
+TODO: List what packages are required for building the software.
+
+TODO: List what packages are required for running the software.
+
+
+# MinGW
+
+MinGW (comes with Git for Windows) support requires the following:
+
+TODO: FILL IN any requirements