Add fmt example and document version from git tag (#100)

* add VERSION_PREFIX argument

* add fmt example

* add VERSION_PREFIX note to readme

* rollback, add info about determining version from git tag

* rollback version

README.md

@@ -36,6 +36,7 @@ CPMAddPackage(
 
 The origin may be specified by a `GIT_REPOSITORY`, but other sources, such as direct URLs, are [also supported](https://cmake.org/cmake/help/v3.11/module/ExternalProject.html#external-project-definition).
 If `GIT_TAG` hasn't been explicitly specified it defaults to `v(VERSION)`, a common convention for git projects.
+On the other hand, if `VERSION` hasn't been explicitly specified, CPM can automatically identify the version from the git tag in some common cases. 
 `GIT_TAG` can also be set to a specific commit or a branch name such as `master` to always download the most recent version.
 The optional argument `FIND_PACKAGE_ARGUMENTS` can be specified to a string of parameters that will be passed to `find_package` if enabled (see below).
 

cmake/CPM.cmake

@@ -124,7 +124,7 @@ function(CPMAddPackage)
     OPTIONS
   )
 
-  cmake_parse_arguments(CPM_ARGS "" "${oneValueArgs}" "${multiValueArgs}" ${ARGN})
+  cmake_parse_arguments(CPM_ARGS "${options}" "${oneValueArgs}" "${multiValueArgs}" "${ARGN}")
 
   if(CPM_USE_LOCAL_PACKAGES OR CPM_LOCAL_PACKAGES_ONLY)
     cpm_find_package(${CPM_ARGS_NAME} "${CPM_ARGS_VERSION}" ${CPM_ARGS_FIND_PACKAGE_ARGUMENTS})

examples/fmt/CMakeLists.txt

@@ -0,0 +1,19 @@
+cmake_minimum_required(VERSION 3.14 FATAL_ERROR)
+
+project(CPMJSONExample)
+
+# ---- Dependencies ----
+
+include(../../cmake/CPM.cmake)
+
+CPMAddPackage(
+  NAME fmt
+  GIT_TAG 6.1.2
+  GITHUB_REPOSITORY fmtlib/fmt
+)
+
+# ---- Executable ----
+
+add_executable(CPMFmtExample "main.cpp")
+set_target_properties(CPMFmtExample PROPERTIES CXX_STANDARD 17)        
+target_link_libraries(CPMFmtExample fmt)

examples/fmt/main.cpp

@@ -0,0 +1,6 @@
+#include <fmt/format.h>
+
+int main(){
+  fmt::print("Hello, {}!\n", "world");
+  return 0;
+}