added cmake module to search for readline

cmake/Modules/Findreadline.cmake

+# Search for the path containing library's headers
+find_path( readline_ROOT_DIR NAMES include/readline/readline.h )
+
+# Search for include directory
+find_path( readline_INCLUDE_DIR NAMES readline/readline.h
+                                HINTS ${Readline_ROOT_DIR}/include )
+
+# Search for library
+find_library( readline_LIBRARY NAMES readline
+                               HINTS ${Readline_ROOT_DIR}/lib )
+
+# use a macro provided by CMake to check if all the listed arguments are valid and set readline_FOUND accordingly
+include(FindPackageHandleStandardArgs)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(readline DEFAULT_MSG readline_INCLUDE_DIR readline_LIBRARY )
+