Improve Makefile & shell configs

* Add cross platform support in Makefile

 * Add host-specific configurations support.

_zshrc

@@ -109,7 +109,17 @@ unsetopt correct_all
 export VISUAL=vi
 export EDITOR=vi
 
+# Host-specific definitions
+if [ -f "${HOME}/.host.zshrc" ]; then
+    . "${HOME}/.host.zshrc"
+fi
+
 # Alias definitions
 if [ -f "${HOME}/.bash_aliases" ]; then
     . "${HOME}/.bash_aliases"
 fi
+
+# Host-specific alias definitions
+if [ -f "${HOME}/.host.aliases" ]; then
+    . "${HOME}/.host.aliases"
+fi