Add metadata file.

meta/libraries.json

@@ -0,0 +1,14 @@
+{
+    "key": "mpl",
+    "name": "MPL",
+    "authors": [
+        "Aleksey Gurtovoy"
+    ],
+    "description": "The Boost.MPL library is a general-purpose, high-level C++ template metaprogramming framework of compile-time algorithms, sequences and metafunctions. It provides a conceptual foundation and an extensive set of powerful and coherent tools that make doing explict metaprogramming in C++ as easy and enjoyable as possible within the current language.",
+    "category": [
+        "Metaprogramming"
+    ],
+    "maintainers": [
+        "Aleksey Gurtovoy <agurtovoy -at- meta-comm.com>"
+    ]
+}