Adding bazel build targets (#251)

Adding support for the bazel build system

.gitignore

@@ -6,3 +6,4 @@ CMakeFiles/
 Testing/
 CTestTestfile.cmake
 cmake_install.cmake
+bazel-*

BUILD

@@ -0,0 +1,8 @@
+load("@rules_cc//cc:defs.bzl", "cc_library")
+
+cc_library(
+    name = "cxxopts",
+    hdrs = ["include/cxxopts.hpp"],
+    strip_include_prefix = "include",
+    visibility = ["//visibility:public"],
+)