ruby: define 'Repository#rebuild_history_file()'
ruby: anhance to support '-b' (rebuild history file) to 'hist' action
ruby: update 'README.md' (and 'Migr8::README', too)
Merge branch 'feature_histrebuild' into ruby-dev
ruby: define 'Skeleton' class
ruby: define 'DBMS::Base#new_skeleton()'
ruby: define 'DBMS::SQLite3::Skeleton' class
ruby: change 'Repository#render_migration_file()' to create skeleton and render with it
ruby: define 'DBMS::PostgreSQL::Skeleton' class
ruby: define 'DBMS::MySQL::Skeleton' class
ruby: rename 'BaseSkeleton#section_xxx()' to '#_section_xxx()'
ruby: remove 'DBMS::SQLite3#skeleton_for_{up,down}()'
Merge branch 'feature_skeletonclass' into ruby-dev