Install locally by default to avoid naively overwriting /usr/local (#52)

Use `-DCMAKE_INSTALL_PREFIX=...` to set a non-local install
destination.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

CMakeLists.txt

@@ -1,8 +1,18 @@
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 3.10)
 project(pystring LANGUAGES CXX VERSION 1.1.4)
 
 option (BUILD_SHARED_LIBS "Build shared libraries (set to OFF to build static libs)" ON)
 
+# If the user hasn't configured cmake with an explicit
+# -DCMAKE_INSTALL_PREFIX=..., then set it to safely install into ./dist, to
+# help prevent the user from accidentally writing over /usr/local or whatever.
+if (CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT
+      AND PROJECT_IS_TOP_LEVEL)
+    set (CMAKE_INSTALL_PREFIX "${PROJECT_SOURCE_DIR}/dist" CACHE PATH
+         "Installation location" FORCE)
+endif()
+message (STATUS "Installation path will be ${CMAKE_INSTALL_PREFIX}")
+
 add_library(pystring
     pystring.cpp
     pystring.h