Initial depends addition

Depends cross compiles project dependencies for linux, mac and windows and multiple architectures.
Depends is original work by Cory Fields and used in bitcoin and a wide range of bitcoin related projects.

contrib/depends/packages/xproto.mk

@@ -0,0 +1,21 @@
+package=xproto
+$(package)_version=7.0.26
+$(package)_download_path=http://xorg.freedesktop.org/releases/individual/proto
+$(package)_file_name=$(package)-$($(package)_version).tar.bz2
+$(package)_sha256_hash=636162c1759805a5a0114a369dffdeccb8af8c859ef6e1445f26a4e6e046514f
+
+define $(package)_set_vars
+$(package)_config_opts=--disable-shared
+endef
+
+define $(package)_config_cmds
+  $($(package)_autoconf)
+endef
+
+define $(package)_build_cmds
+  $(MAKE)
+endef
+
+define $(package)_stage_cmds
+  $(MAKE) DESTDIR=$($(package)_staging_dir) install
+endef