[sledge] Add convenience links to executables

Summary:
The names of the compiled sledge executables are long, which is
inconvenient. Also, all build modes produce an executable named
`sledge`, so it is not possible to add them to PATH and still be able
to run the desired executable. This diff adds a directory of symbolic
links with different names that refer to the executables built in the
different build modes. The intent is for people to add .../sledge/bin
to their PATH.

Reviewed By: jvillard

Differential Revision: D27315805

fbshipit-source-id: 7e84e43a7

sledge/bin/sledge

@@ -0,0 +1 @@
+../_build/_install/release/bin/sledge

sledge/bin/sledge.dbg

@@ -0,0 +1 @@
+../_build/_install/debug/bin/sledge

sledge/bin/sledge.trc

@@ -0,0 +1 @@
+../_build/_install/trace/bin/sledge