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/MapsTest.cpp b/libunwindstack/tests/MapsTest.cpp
index 7eb9bae..9430cf3 100644
--- a/libunwindstack/tests/MapsTest.cpp
+++ b/libunwindstack/tests/MapsTest.cpp
@@ -20,7 +20,9 @@
 #include <android-base/test_utils.h>
 #include <gtest/gtest.h>
 
-#include "Maps.h"
+#include <unwindstack/Maps.h>
+
+namespace unwindstack {
 
 TEST(MapsTest, parse_permissions) {
   BufferMaps maps(
@@ -235,3 +237,5 @@
   ASSERT_EQ(PROT_READ | PROT_WRITE | PROT_EXEC, info->flags);
   ASSERT_EQ("/system/lib/fake5.so", info->name);
 }
+
+}  // namespace unwindstack