Doit

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- fix 38: `doit.tools.create_folder()` raise error if file exists in path
- `create_doit_tasks` not called for unbound methods
- support execution using "python -m doit"
- fix 33: Failing to clean a group of task(s) with sub-tasks
- python-actions can take a magic "task" parameter as reference to task
- expose task.clean_targets
- tools.PythonInteractiveAction saves "result" and "values"
- fix 40. added option to use threads for parallel running of tasks
- same code base for python 2 & 3 (no need to use tool `2to3`)
- add sqlite3 DB backend
- added option to select backend

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- added command `dumpdb`
- added `CmdAction.save_out` param
- `CmdAction` support for callable that returns a command string
- BACKWARD INCOMPATIBLE `getargs` for a group task gets a dict where
each key is the name of subtasks (previously it was a list)
- added command `strace`
- cmd `auto` run tasks on separate process
- support unicode for task name

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- support for `doit help <task-name>`
- added support to load tasks using `create_doit_tasks`
- dropped python 2.5 support

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- fix bug cmd option --continue not being recognized

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- remove DEPRECATED `Task.insert_action`, `result_dep` and `getargs` using strings
- fix 10 --continue does not execute tasks that have failed dependencies
- fix --always-execute does not execute "ignored" tasks
- fix 29 python3 cmd-actions issue
- fix 30 tests pass on all dbm backends
- API to add new sub-commands to doit
- API to modify task loader
- API to make dodo.py executable
- added ZeroReporter

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- fix 12 Action.out and Action.err not set when using multiprocessing
- fix 16 fix `forget` command on gdbm backend
- fix 14 improve parallel execution (better process utilization)
- fix 9 calc_dep create implicit task_dep if a file_dep returned is a also a target
- added tools.result_dep
- fix 15 tools.result_dep supports group-tasks
- DEPRECATE task attribute `result_dep` (use tools.result_dep)
- DEPRECATE `getargs` specification using strings (must use 2-element tuple)
- several changes on `uptodate`
- DEPRECATE `Task.insert_action` (replaced by `Task.value_savers`)
- fix 8 `clean` cleans all subtasks from a group-task
- fix 8 `clean` added flag `--all` to clean all tasks
- fix 8 `clean` when no task is specified set --clean-dep and clean default tasks