CMake option to disable tests compilation

[01e9]

First of all thank you for making this library installable. I use External_Project_Add() for all libraries, it compiles the library in an isolated environment and installs it in the specified directory (if you are interested in more details I can explain).

What I want is a way to disable tests when building the library.

Wrap this block in an if

thread-pool-cpp/CMakeLists.txt

Lines 11 to 22 in af95dd8

	# gtest
	enable_testing()
	add_subdirectory(googletest)
	include_directories(${CMAKE_CURRENT_SOURCE_DIR}/googletest/googletest/include)
	include_directories(${CMAKE_CURRENT_SOURCE_DIR}/include)
	# Tests
	add_subdirectory(tests)
	# Benchmark
	add_subdirectory(benchmark)

like this

https://github.com/Microsoft/GSL/blob/5cbde3008aa43a9c5f6c219ee15b8388336d4433/CMakeLists.txt#L71-L75

then I will be able to control that block with -DENABLE_TESTS=ON/OFF