add unit tests and determine version from GIT_TAG (#66)

* add unit tests

* determine package version from git tag. closes #54.

* update readme

* bugfix

* update example

* update gitignore

test/CMakeLists.txt

@@ -0,0 +1,14 @@
+cmake_minimum_required(VERSION 3.14 FATAL_ERROR)
+
+file(GLOB tests "${CMAKE_CURRENT_SOURCE_DIR}/unit/*.cmake")
+
+enable_testing()
+
+foreach(test ${tests})
+  message(STATUS "adding test: ${test}")
+  add_test(
+    NAME ${test} 
+    COMMAND ${CMAKE_COMMAND} -DCPM_PATH=${CMAKE_CURRENT_SOURCE_DIR}/../cmake -P "${test}"
+  )
+
+endforeach()