move remain contsnt and method to BuildSystem
refactor - move build related file and rule task to BuildSystem
refactor - extract task definition methods
move retrieving source file to BuildSystem::build
create BuildSystem instance in each build task
implement clear and clobber task myself
move methods that don't be called from external to private
refactor - extract setup compiler method
change constants in BuildSystem into instance variables
create BuildConfig class manages build configuration settings
redesign BuildSystem

remove BuildConfig class and define tasks in BuildSystem.
remove default task for namespace adding
add namespace to tasks in BuildSystem
move compile flags and others to top level for sharing with other build
change build system name for server