Organize LLVM C API docs into doxygen modules; add docs

This gives a lot of love to the docs for the C API. Like Clang's
documentation, the C API is now organized into a Doxygen "module"
(LLVMC). Each C header file is a child of the main module. Some modules
(like Core) have a hierarchy of there own. The produced documentation is
thus better organized (before everything was in one monolithic list).

This patch also includes a lot of new documentation for APIs in Core.h.
It doesn't document them all, but is better than none. Function docs are
missing @param and @return annotation, but the documentation body now
commonly provides help details (like the expected llvm::Value sub-type
to expect).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153157 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/llvm-c/EnhancedDisassembly.h b/include/llvm-c/EnhancedDisassembly.h
index 0c173c2..71a0d49 100644
--- a/include/llvm-c/EnhancedDisassembly.h
+++ b/include/llvm-c/EnhancedDisassembly.h
@@ -25,6 +25,19 @@
 extern "C" {
 #endif
 
+/**
+ * @defgroup LLVMCEnhancedDisassembly Enhanced Disassembly
+ * @ingroup LLVMC
+ * @deprecated
+ *
+ * This module contains an interface to the Enhanced Disassembly (edis)
+ * library. The edis library is deprecated and will likely disappear in
+ * the near future. You should use the @ref LLVMCDisassembler interface
+ * instead.
+ *
+ * @{
+ */
+
 /*!
  @typedef EDByteReaderCallback
  Interface to memory from which instructions may be read.
@@ -504,6 +517,10 @@
 int EDBlockVisitTokens(EDInstRef inst,
                        EDTokenVisitor_t visitor);
 
+/**
+ * @}
+ */
+
 #endif
 
 #ifdef __cplusplus