Add regular expression filters

[johnlettman]

This PR adds regular expression filters per #1.

A significant concern is the balancing of user input sanitization vs. flexibility. Regular expressions could cause a ReDoS vector without filtering if the tool is used upstream in other projects. However, filtering removes groups, or operators, * extensions, and more, essentially making regular expressions useless.

I have used timeouts to prevent long-running regular expressions (e.g., preventing ReDoS through execution limits). This required the non-standard-library package regex, which provides timeouts.

The new filters are:

• / -> REGEX
• ^/ -> NOT_REGEX

The new info page is:

+----+
|NOTE|
+----+
Jockey is a work-in-progress currently only supports querying:
    units
    machines


+-------+
|FILTERS|
+-------+
Filters have a three-part syntax:
    <object type><filter code><content>

<object type> can be any supported Juju object types or their equivalent
abbreviations (see "SHORT NAMES", below).  These values are identical to the
`object` argument in the Jockey CLI.

<filter code> specifies how objects should be filtered relative to <content>
There are four possible values for <filter code>:
    =  : matches
    ^= : does not match
    ~  : contains
    ^~ : does not contain
    /  : matches regex
    ^/ : does not match regex
Exactly one <filter code> must be given per filter.

<content> is a given string that will be used to filter Juju object names.


+-----------+
|SHORT NAMES|
+-----------+
Jockey object name abbreviations:

OBJECT TYPE    SHORT NAMES
charms         charm, c
applications   app, apps, application, a
units          unit, u
machines       machine, m
ips            address, addresses, ip, i
hostnames      hostname, host, hosts, h


+---------------+
|EXAMPLE QUERIES|
+---------------+
 Get all units:
     jockey units

 Get all nova-compute units:
     jockey units application=nova-compute

 Get the hw-health unit on a machine with a partial hostname "e01":
    jockey u a=hw-health host~e01

 Get all non-lxd machines:
     jockey m m^~lxd

 Get units for applications matching a regular expression:
     jockey u a/'telegraf-ceph-(osd|mon)'


+-------------------+
|OPERATIONS EXAMPLES|
+-------------------+
 Run a 'show-sel' action a machine with a partial host name 'ts1363co':
     juju run-action --wait $(jockey u a~hw-hea m~ts1363co) show-sel

[johnlettman]

Ah, missing tests. I will get to that shortly.

[johnlettman]

Closing: this will be included in a larger overall refactor I'm developing.

[LCVcode]

Okay. What are you planning to refactor?

[johnlettman]

#47 complex caching and deeper introspection