Make sure all classes are in 'peloton' namespace

[apavlo]

All of the C++ files in the src directory that we wrote should be under the peloton namespace. If it is a third-party file, then it should be moved to the third_party directory. Here are the files that are not in the proper namespace:

$ grep -Lr "namespace peloton" src/ | grep -P "(\.h|\.cpp)"
src/include/index/bloom_filter.h
src/include/index/sorted_small_set.h
src/include/index/atomic_stack.h
src/include/common/timer.h
src/include/common/generator.h
src/include/executor/executors.h
src/include/parser/statements.h
src/include/parser/sql_parser.h
src/include/parser/sql_scanner.h
src/main/peloton/peloton.cpp

[wangziqi2013]

I will add the namespace for index components today.

[pbollimp]

Due to multiple code conflicts with everyone, I will create a pull request and merge this after December 27