If a name isn't provided, try to infer it from the git repo (#202)

* Added assert_not_defined check

* Function to get package name form git uri and tests

* Autofix format

* If name is not provided, try to infer it from the git repo

* Unset result of cpm_package_name_from_git_uri if there is no match
- Also reordered tests to ensure that the result is actually unset when needed

* Removed trailing spaces in README

* Updated the main example with the new minimal syntax

* Well... autofix format again

* Update error message for missing name to reflect the possible auto-infer step

* Autofix format... yet again :)

cmake/testing.cmake

@@ -36,6 +36,14 @@ function(ASSERT_DEFINED KEY)
   endif()
 endfunction()
 
+function(ASSERT_NOT_DEFINED KEY)
+  if(DEFINED ${KEY})
+    message(FATAL_ERROR "assertion failed: '${KEY}' is defiend")
+  else()
+    message(STATUS "test passed: '${KEY}' is not defined")
+  endif()
+endfunction()
+
 function(ASSERT_TRUTHY KEY)
   if(${${KEY}})
     message(STATUS "test passed: '${KEY}' is set truthy")