Problem::Evaluate implementation.

1. Add Problem::Evaluate and tests.
2. Remove Solver::Summary::initial/final_*
3. Remove Solver::Options::return_* members.
4. Various cpplint cleanups.

Change-Id: I4266de53489896f72d9c6798c5efde6748d68a47

.gitignore

diff --git a/.gitignore b/.gitignore
index 0f0d1c7..62a4f75 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,6 +7,7 @@
 build/
 build-release/
 build-debug/
+docs/html
 *.aux
 *.blg
 *.toc