Externals: add hidapi

Current master (d17db57b9d4354752e0af42f5f33007a42ef2906) because
Android support was added after the current release (0.8.0-rc1).

Externals/hidapi/testgui/Makefile-manual

@@ -0,0 +1,26 @@
+
+
+OS=$(shell uname)
+
+ifeq ($(OS), Darwin)
+	FILE=Makefile.mac
+endif
+
+ifneq (,$(findstring MINGW,$(OS)))
+	FILE=Makefile.mingw
+endif
+
+ifeq ($(OS), Linux)
+	FILE=Makefile.linux
+endif
+
+ifeq ($(OS), FreeBSD)
+	FILE=Makefile.freebsd
+endif
+
+ifeq ($(FILE), )
+all:
+	$(error Your platform ${OS} is not supported at this time.)
+endif
+
+include $(FILE)