Add support for the CMake build system.

This brings various improvements to the current Makefile and intends to help
people to package WOFF2:

* Build and install static and shared libraries for encoder and decoder
* Install public headers
* Generate and install pc files for PkgConfig
* Build the woff2_* programs
* Build the fuzzer archives
* Specify a release version (0.0.1 is hardcoded for now)
* Build using a Brotli version installed on the system, instead of the git
  submodule
* Have some CANONICAL_PREFIXES and NOISY_LOGGING configuration options

cmake/FindBrotliDec.cmake

@@ -0,0 +1,35 @@
+# Copyright 2017 Igalia S.L. All Rights Reserved.
+#
+# Distributed under MIT license.
+# See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+
+# Try to find BrotliDec. Once done, this will define
+#
+#  BROTLIDEC_FOUND - system has BrotliDec.
+#  BROTLIDEC_INCLUDE_DIRS - the BrotliDec include directories
+#  BROTLIDEC_LIBRARIES - link these to use BrotliDec.
+
+find_package(PkgConfig)
+
+pkg_check_modules(PC_BROTLIDEC libbrotlidec)
+
+find_path(BROTLIDEC_INCLUDE_DIRS
+    NAMES brotli/decode.h
+    HINTS ${PC_BROTLIDEC_INCLUDEDIR}
+)
+
+find_library(BROTLIDEC_LIBRARIES
+    NAMES brotlidec
+    HINTS ${PC_BROTLIDEC_LIBDIR}
+)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(BrotliDec
+    REQUIRED_VARS BROTLIDEC_INCLUDE_DIRS BROTLIDEC_LIBRARIES
+    FOUND_VAR BROTLIDEC_FOUND
+    VERSION_VAR PC_BROTLIDEC_VERSION)
+
+mark_as_advanced(
+    BROTLIDEC_INCLUDE_DIRS
+    BROTLIDEC_LIBRARIES
+)