Updating Catch2

In order to update catch2 the following changes were made:
- CMakeLists.txt: import catch2 with FetchContent_Declare, this will
  make it more flexible and easier to update
- removed main for tests, since it is not mandatory and it doesn't add
  any value of having it
- renaming includes in all the files

Author: andreagilardoni

Diff for: test/CMakeLists.txt

@@ -8,11 +8,20 @@ cmake_minimum_required(VERSION 2.8)
 
 project(test-ArduinoCore-API)
 
+Include(FetchContent)
+
+FetchContent_Declare(
+  Catch2
+  GIT_REPOSITORY https://github.com/catchorg/Catch2.git
+  GIT_TAG        v3.4.0
+)
+
+FetchContent_MakeAvailable(Catch2)
+
 ##########################################################################
 
 include_directories(..)
 include_directories(include)
-include_directories(external/catch/v2.13.9/include)
 
 ##########################################################################
 
@@ -118,7 +127,6 @@ set(TEST_DUT_SRCS
 ##########################################################################
 
 set(TEST_TARGET_SRCS
-  src/main.cpp
   src/dtostrf.cpp
   src/itoa.cpp
   src/MillisFake.cpp
@@ -144,5 +152,7 @@ add_executable(
   ${TEST_TARGET_SRCS}
 )
 
+target_link_libraries( ${TEST_TARGET} Catch2WithMain )
+
 ##########################################################################