Include some examples of --select.

[tomprince]

It isn't clear how to write useful queries for `--select``, just from looking at the linked documentation.

[jonathanj]

@tomprince Can you give an example of something you were trying to use --select to achieve? I could include some examples of how I've used it but I have no idea if it is useful to anyone else, a better idea of what others are trying to find would help.

[exarkun]

I wanted to select a date range using select. With idnar's help I got as far as this:

eliot-tree --select "timestamp > date(\`$(date --date '2015-10-29 12:45:16+0000' +%s)\`)" --select "timestamp < \`$(date --date '2015-10-29 12:47:16+0000' +%s)\`"

The need to use another tool to convert from the formatted timestamps I'm starting with is a bit annoying. It would be cool if I could just give them to Eliot as-is and let it sort out that they're timestamps.

The extra backticks required were kind of annoying too, but I guess that's just how jmespath works...

But the real kicker is that this doesn't actually work:

Traceback (most recent call last):
  File "/home/jean-paul/Environments/flocker/bin/eliot-tree", line 11, in <module>
    sys.exit(main())
  File "/home/jean-paul/Environments/flocker/local/lib/python2.7/site-packages/eliottree/_cli.py", line 108, in main
    display_task_tree(args)
  File "/home/jean-paul/Environments/flocker/local/lib/python2.7/site-packages/eliottree/_cli.py", line 58, in display_task_tree
    human_readable=args.human_readable)
  File "/home/jean-paul/Environments/flocker/local/lib/python2.7/site-packages/eliottree/_cli.py", line 46, in build_task_nodes
    return tree.nodes(tree.merge_tasks(tasks, filter_funcs()))
  File "/home/jean-paul/Environments/flocker/local/lib/python2.7/site-packages/eliottree/tree.py", line 176, in merge_tasks
    pending = _merge(tasks)
  File "/home/jean-paul/Environments/flocker/local/lib/python2.7/site-packages/eliottree/tree.py", line 172, in _merge
    if fn(task):
  File "/home/jean-paul/Environments/flocker/local/lib/python2.7/site-packages/eliottree/filter.py", line 10, in _filter
    return bool(expn.search(task))
  File "/home/jean-paul/Environments/flocker/local/lib/python2.7/site-packages/jmespath/parser.py", line 524, in search
    result = interpreter.visit(self.parsed, value)
  File "/home/jean-paul/Environments/flocker/local/lib/python2.7/site-packages/jmespath/visitor.py", line 66, in visit
    return method(node, *args, **kwargs)
  File "/home/jean-paul/Environments/flocker/local/lib/python2.7/site-packages/jmespath/visitor.py", line 115, in visit_comparator
    self.visit(node['children'][1], value)
TypeError: can't compare datetime.datetime to int