Make the library usable as a library.

- Add namespace unwindstack everywhere so that it's easier for other
  code to use the library.
- Move some of the header files into include/unwindstack so that they
  can be exposed.
- Modify the headers so that only a limited number need to be exposed.
- Update the tools to use the new headers.
- Add a GetLoadBias() call on the Elf object. This prevents the need
  to get the interface object out of the Elf object.
- Move the GetRelPc() call out of the Reg class, to the Elf class. It's
  not always the case that a Reg object will be around when you want to
  get a relative pc. The tests for this moved to ElfTest.cpp.

Bug: 23762183

Test: Unit tests pass.
Change-Id: Iac609dac1dd90ed83d1a1e24ff2579c96c023bc3
diff --git a/libunwindstack/tests/MapInfoGetElfTest.cpp b/libunwindstack/tests/MapInfoGetElfTest.cpp
index fc36cc6..abfa172 100644
--- a/libunwindstack/tests/MapInfoGetElfTest.cpp
+++ b/libunwindstack/tests/MapInfoGetElfTest.cpp
@@ -30,9 +30,13 @@
 #include <android-base/test_utils.h>
 #include <gtest/gtest.h>
 
-#include "Elf.h"
+#include <unwindstack/Elf.h>
+#include <unwindstack/MapInfo.h>
+#include <unwindstack/Memory.h>
+
 #include "ElfTestUtils.h"
-#include "MapInfo.h"
+
+namespace unwindstack {
 
 class MapInfoGetElfTest : public ::testing::Test {
  protected:
@@ -138,3 +142,5 @@
   EXPECT_EQ(ELFCLASS64, elf->class_type());
   EXPECT_TRUE(elf->gnu_debugdata_interface() != nullptr);
 }
+
+}  // namespace unwindstack