Add NEWS, doc for string and command macros

Author: TotalVerb

NEWS.md

@@ -24,6 +24,14 @@ Language changes
     This can be changed back to the original color by setting the environment variable `JULIA_INFO_COLOR` to `"blue"`.
     One way of doing this is by adding `ENV["JULIA_INFO_COLOR"] = :blue` to the `.juliarc.jl` file.
     For more information regarding customizing colors in the REPL, see this [manual section]( http://docs.julialang.org/en/latest/manual/interacting-with-julia/#customizing-colors).
+  * Multiline and singleline command macros have been added. A command macro is
+    like a string macro, but the syntax uses backquotes (<code>`</code>)
+    instead of double quotes, and the resulting macro called is suffixed with
+    `_cmd`. For instance, the syntax <code>q`xyz`</code> is equivalent to
+    `@q_cmd "xyz"`.
+  * String and command macros can now be qualified with their module. For
+    instance, `Base.r"x"` is now parsed as `Base.@r_str "x"`. Previously, this
+    syntax parsed as an implicit multiplication.
 
 Breaking changes
 ----------------

doc/manual/metaprogramming.rst

@@ -864,13 +864,27 @@ majority of use cases, however, regular expressions are not constructed
 based on run-time data. In this majority of cases, the ability to write
 regular expressions as compile-time values is invaluable.
 
+Like non-standard string literals, non-standard command literals exist using a
+prefixed variant of the command literal syntax. The command literal
+``custom`literal``` is parsed as ``@custom_cmd "literal"``. Julia itself does
+not contain any non-standard command literals, but packages can make use of
+this syntax. Aside from the different syntax and the ``_cmd`` suffix instead of
+the ``_str`` suffix, non-standard command literals behave exactly like
+non-standard string literals.
+
+In the event that two modules provide non-standard string or command literals
+with the same name, it is possible to qualify the string or command literal
+with a module name. For instance, if both ``Foo`` and ``Bar`` provide
+non-standard string literal ``@x_str``, then one can write ``Foo.x"literal"``
+or ``Bar.x"literal"`` to disambiguate between the two.
+
 The mechanism for user-defined string literals is deeply, profoundly
 powerful. Not only are Julia's non-standard literals implemented using
 it, but also the command literal syntax (```echo "Hello, $person"```)
 is implemented with the following innocuous-looking macro::
 
     macro cmd(str)
-      :(cmd_gen($shell_parse(str)))
+      :(cmd_gen($(shell_parse(str)[1])))
     end
 
 Of course, a large amount of complexity is hidden in the functions used