Various improvements and fixes.

 - per user directory for log files.
 - potential race in base.MakeDirs().
 - include timezone in logs.
 - memoize and synchronized decorators.
 - float and boolean flag types.
ImmutableDict : immutable version of dict().
Generic workflow of tasks with dependencies.

 - Custom persistent tasks on local FS.
Unique ID for shell commands
Some fixes
Tweak logging
More tweaks
Include global flags when printing CLI specific flags help.
Multi-threaded HTTP server base class.
Very simply workflow monitoring interface.

 - Relies on Graphviz/Dot to generate an SVG diagram.
HTTP endpoint to dump workflow as dot definition
Add log statement
Table representation of a workflow
Sort task lists
Introduce constant base.Undefined
Dictionary-like and object-like record.
Base class for tasks with inputs and outputs.
Fix crash with undocumented flags
Release to pypi.

 - Add hierarchical flags.
Fix UnCamelCase