Buildscript and kernel improvements (#280)

- Implemented `constexpr long int getMicros()` in `Kernel.h`
- Changed `secondsToTicks()`, `minutesToTicks()` and `bool isIsr()` to `constexpr`
- Added more relevant build info

Buildscripts/colors.cmake

@@ -0,0 +1,14 @@
+if (NOT WIN32)
+    string(ASCII 27 Esc)
+    set(ColorReset "${Esc}[m")
+    set(Cyan        "${Esc}[36m")
+    set(Grey        "${Esc}[37m")
+    set(LightPurple "${Esc}[1;35m")
+    set(White       "${Esc}[1;37m")
+else ()
+    set(ColorReset "")
+    set(Cyan        "")
+    set(Grey        "")
+    set(LightPurple "")
+    set(White       "")
+endif ()