Documentation & Logging cleanups.

1. Document the use of dogleg and a general discussion of
   trust region methods.
2. Added a TBD section on compiler/linker flags.
3. Summary::FullReport now prints out sparse_linear_algebra_library
   and trust_region_strategy_type.

Change-Id: I01f680070d510715900f345364855689005d54bb

.gitignore

@@ -5,6 +5,8 @@ CMakeLists.txt.user*
 *.bak
 *.orig
 build/
+build-release/
+build-debug/
 *.aux
 *.blg
 *.toc