Add support for Bazel build system

[mglb]

Adds support for using JsonCpp as an external package in Bazel projects.

Tested in https://github.com/google/verible by replacing:

http_archive(
    name = "jsoncpp_git",
    sha256 = "77a402fb577b2e0e5d0bdc1cf9c65278915cdb25171e3452c68b6da8a561f8f0",
    build_file = "//bazel:jsoncpp.BUILD",
    strip_prefix = "jsoncpp-1.9.2",
    urls = [
        "https://github.com/open-source-parsers/jsoncpp/archive/1.9.2.tar.gz",
    ],
)

with:

git_repository(
    name = "jsoncpp_git",
    branch = "mglb/bazel-support",
    remote = "https://github.com/mglb/jsoncpp.git",
)

in WORKSPACE file, and then running bazel clean; bazel test //...

[baylesj]

Not sure why the build is failing, I'm wondering if it is a fluke?

[mglb]

Name conflict. The CI has been building in build folder, but now BUILD is a file in the repo.
I've changed the build folder name.

[cdunn2001]

We're very happy to include support for Bazel. Thank you!

[cdunn2001]

Why build_out for cmake? Is that to be consistent with a bagel folder?

[mglb]

Name conflict. The CI has been building in build folder, but now BUILD is a file in the repo.

Anyway, I've removed this change and renamed the Bazel file to BUILD.bazel. This name is less popular, but officialy recognized by Bazel.

[cdunn2001]

I'd like to keep README.md short and move as much as possible to our wiki? The reason is simple: To avoid doc-only changes in the source-code repo.

[mglb]

Removed

[mglb]

Note to be added to the wiki:

The Bazel build system

To use specific JsonCpp version in your Bazel project, edit your WORKSPACE file and add a http_archive rule:

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
# ...
http_archive(
    name = "jsoncpp",
    # sha256 = "X.Y.Z.tar.gz SHA256",
    strip_prefix = "jsoncpp-X.Y.Z",
    urls = [
        "https://github.com/open-source-parsers/jsoncpp/archive/X.Y.Z.tar.gz",
    ],
)

Replace X.Y.Z with a correct version, and optionally specify archive file's SHA256 hash.
To get the code directly from a git repository, add a git_repository instead:

load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
# ...
git_repository(
    name = "jsoncpp",
    branch = "master",
    remote = "https://github.com/open-source-parsers/jsoncpp.git",
)

In either case, add "@jsoncpp//:jsoncpp" as a dependency to targets that use JsonCpp.

[cdunn2001]

The commits seem to be gone. Rebase maybe?

[mglb]

@cdunn2001
Branch rebased, everything seems to be working.

[cdunn2001]

Copied to wiki. Thanks!