Fix bazel installer bash script (#33)

Udate grpc/protobuf/abseil version. lock bazel version.

Add --config=clang to build with prebuilt clang compiler.

Add clang_toolchain to download prebuilt clang binaries.

Update grpc to 1.36.x branch.

use https instead git access

Use //tools/build_rules:boost.bzl inside boost/BUILD

Fix run under.

Depend on gflag since glog doesn't depend on gflags any more.

use bazel 3.6.0.

Upgrade grpc/protobuf to the latest release, update zlib/abseil to the

drop is_library from boost.bzl

update glog and gtest deps for folly.

Add base/init.{h,cc} with BUILD file. update examples.

Switch glog to bazelment, switch gtest to use the built-in bazel build files.