Updates for Documenter.jl syntax changes

See https://github.com/MichaelHatherly/Documenter.jl/pull/51 for details.

doc/src/chunk_options.md

@@ -57,7 +57,8 @@ Weave.set_chunk_defaults(Dict{Symbol, Any}(
 ```
 
 
-    {docs}
-      set_chunk_defaults(opts)
-      get_chunk_defaults()
-      restore_chunk_defaults()
+```@docs
+set_chunk_defaults(opts)
+get_chunk_defaults()
+restore_chunk_defaults()
+```

doc/src/function_index.md

@@ -1,4 +1,5 @@
 
 # Function index
 
-    {index}
+```@index
+```

doc/src/index.md

@@ -19,4 +19,5 @@ and Sweave.
 
 ## Contents
 
-    {contents}
+```@contents
+```

doc/src/usage.md

@@ -18,8 +18,9 @@ Using PyPlot:
 weave(Pkg.dir("Weave","examples","julia_sample.mdw"), plotlib="PyPlot", out_path = :pwd)
 ```
 
-    {docs}
-      weave(source)
+```@docs
+weave(source)
+```
 
 ## Weave from shell
 
@@ -37,9 +38,9 @@ usage: weave.jl [--doctype DOCTYPE] [--plotlib PLOTLIB]
 
 Tangling extracts the code from document:
 
-    {docs}
-      tangle(source)
-
+```@docs
+tangle(source)
+```
 
 ## Supported formats
 
@@ -70,8 +71,9 @@ asciidoc: AsciiDoc
 tex: Latex with custom code environments
 ```
 
-    {docs}
-      list_out_formats()
+```@docs
+list_out_formats()
+```
 
 ## Document syntax