added lua and _lua

sheets/_lua/hello

@@ -0,0 +1,11 @@
+-- to install: 
+--   (Debian/Ubuntu) apt-get install lua
+--   (Fedora/CentOS) yum install lua
+--   (source code)   curl -R -O http://www.lua.org/ftp/lua-5.3.4.tar.gz | tar xz - 
+--                   cd lua-5.3.4
+--                   make linux
+--
+-- to execute: 
+--   lua hello.lua
+
+io.write("Hello world, from ",_VERSION,"!\n")

sheets/lua

@@ -0,0 +1,21 @@
+# lua
+# A powerful, light-weight embeddable programming language.
+
+# Start an interactive Lua shell:
+lua
+
+# Execute a Lua script:
+lua script_name.lua --optional-argument
+
+# Execute a Lua expression:
+lua -e 'print( "Hello World" )'
+
+# All options are handled in order, except -i. For instance, an invocation like
+# first set a to 1, then print the value of a (1), and finally run the file script.lua
+lua -e'a=1' -e 'print(a)' script.lua
+
+# See also:
+#   Lua language cheat sheets at /lua/
+#   list of pages:      /lua/:list
+#   learn lua:          /lua/:learn
+#   search in pages:    /lua/~keyword