Added pkgconfig support

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index ffbf23d..8933b11 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -27,6 +27,9 @@
   option(EIGEN_BUILD_LIB "Build the binary shared library" OFF)
 endif(NOT WIN32)
 option(EIGEN_BUILD_BTL "Build benchmark suite" OFF)
+if(NOT WIN32)
+  option(EIGEN_BUILD_PKGCONFIG "Build pkg-config .pc file for Eigen" ON)
+endif(NOT WIN32)
 
 if(EIGEN_BUILD_LIB)
   option(EIGEN_TEST_LIB "Build the unit tests using the library (disable -pedantic)" OFF)
@@ -98,6 +101,13 @@
     "The directory where we install the header files"
     FORCE)
 
+if(EIGEN_BUILD_PKGCONFIG)
+    configure_file(eigen2.pc.in eigen2.pc)
+    install(FILES eigen2.pc
+        DESTINATION lib/pkgconfig
+        )
+endif(EIGEN_BUILD_PKGCONFIG)
+
 add_subdirectory(Eigen)
 
 add_subdirectory(doc)
@@ -119,4 +129,4 @@
 
 if(EIGEN_BUILD_TESTS)
   ei_testing_print_summary()
-endif(EIGEN_BUILD_TESTS)
\ No newline at end of file
+endif(EIGEN_BUILD_TESTS)

eigen2.pc.in

diff --git a/eigen2.pc.in b/eigen2.pc.in
new file mode 100644
index 0000000..b508a58
--- /dev/null
+++ b/eigen2.pc.in
@@ -0,0 +1,7 @@
+
+Name: Eigen2
+Description: A C++ template library for linear algebra: vectors, matrices, and related algorithms
+Requires:
+Version: ${EIGEN_VERSION_NUMBER}
+Libs:
+Cflags: -I${INCLUDE_INSTALL_DIR}