doc: Convert INSTALL instructions to Markdown

INSTALL.md

+Installing a binary distribution package
+========================================
+
+No official binary distribution packages are provided by the gflags developers.
+There may, however, be binary packages available for your OS. Please consult
+also the package repositories of your Linux distribution.
+
+For example on Debian/Ubuntu Linux, gflags can be installed using the
+following command:
+
+    sudo apt-get install gflags
+
+
+Compiling the source code
+=========================
+
+The build system of gflags is since version 2.1 based on [CMake](http://cmake.org).
+The common steps to build, test, and install software are therefore:
+
+1. Extract source files.
+2. Create build directory and change to it.
+3. Run CMake to configure the build tree.
+4. Build the software using selected build tool.
+5. Test the built software.
+6. Install the built files.
+
+On Unix-like systems with GNU Make as build tool, these build steps can be
+summarized by the following sequence of commands executed in a shell,
+where ```$package``` and ```$version``` are shell variables which represent
+the name of this package and the obtained version of the software.
+
+    $ tar xzf gflags-$version-source.tar.gz
+    $ cd gflags-$version
+    $ mkdir build && cd build
+    $ ccmake ..
+    
+      - Press 'c' to configure the build system and 'e' to ignore warnings.
+      - Set CMAKE_INSTALL_PREFIX and other CMake variables and options.
+      - Continue pressing 'c' until the option 'g' is available.
+      - Then press 'g' to generate the configuration files for GNU Make.
+    
+    $ make
+    $ make test    (optional)
+    $ make install (optional)
+
+In the following, only gflags-specific CMake settings available to
+configure the build and installation are documented.
+
+
+CMake Option           | Description
+---------------------- | -------------------------------------------------------
+CMAKE_INSTALL_PREFIX   | Installation directory, e.g., "/usr/local" on Unix and "C:\Program Files\gflags" on Windows.
+GFLAGS_NAMESPACE       | Name of the C++ namespace to be used by the gflags library. Note that the public source header files are installed in a subdirectory named after this namespace. To maintain backwards compatibility with the Google Commandline Flags, set this variable to "google". The default is "gflags".
+GFLAGS_INCLUDE_DIR     | Name of include subdirectory where headers are installed into.

INSTALL.txt

-
-INSTALLING A BINARY DISTRIBUTION PACKAGE
-========================================
-
-No official binary distribution packages are provided by the gflags developers.
-There may, however, be binary packages available for your OS at
-https://code.google.com/p/gflags/downloads/list. Please consult also the
-package repositories of your Linux distribution.
-
-For example on Debian/Ubuntu Linux, gflags can be installed using the
-following command:
-
-$ sudo apt-get install gflags
-
-
-
-BUILDING THE SOFTWARE FROM SOURCES
-==================================
-
-Build Steps
------------
-
-The build system of gflags is since version 2.1 based on CMake (cmake.org).
-The common steps to build, test, and install software based on CMake are:
-
-1. Extract source files.
-2. Create build directory and change to it.
-3. Run CMake to configure the build tree.
-4. Build the software using selected build tool.
-5. Test the built software.
-6. Install the built files.
-
-On Unix-like systems with GNU Make as build tool, these build steps can be
-summarized by the following sequence of commands executed in a shell,
-where $package and $version are shell variables which represent the name
-of this package and the obtained version of the software.
-
-$ tar xzf gflags-$version-source.tar.gz
-$ cd gflags-$version
-$ mkdir build && cd build
-$ ccmake ..
-
-  - Press 'c' to configure the build system and 'e' to ignore warnings.
-  - Set CMAKE_INSTALL_PREFIX and other CMake variables and options.
-  - Continue pressing 'c' until the option 'g' is available.
-  - Then press 'g' to generate the configuration files for GNU Make.
-
-$ make
-$ make test    (optional)
-$ make install (optional)
-
-In the following, only gflags-specific CMake settings available to
-configure the build and installation are documented.
-
-
-CMake Options
--------------
-
-- CMAKE_INSTALL_PREFIX   Installation directory, e.g., "/usr/local" on Unix
-                         and "C:\Program Files\gflags" on Windows.
-
-
-Advanced CMake Options
-----------------------
-
-- GFLAGS_NAMESPACE   Name of the C++ namespace to be used by the gflags library.
-                     Note that the public source header files are installed in
-                     a subdirectory named after this namespace. To maintain
-                     backwards compatibility with the Google Commandline Flags,
-                     set this variable to "google". The default is "gflags".