Support align and min_width module options

This patch enables users to define "align" and "min_width" options
right in the i3status module config sections.

Specifically this patch:
 * Adds macros for the two new options that are used in the option
   definitions. As the min_width option can take either a string or a
   number, a custom type has been added along with a corresponding callback
   function that parses the provided value (and provides input validation).
   The align option also uses a callback for input validation
 * Expands all module config option definitions to include the new
   options
 * Extends the SEC_CLOSE_MAP() macro to generate the JSON for the new
   options as necessary
 * Updates the manpage to explain the new options
disk: Colorize output when below given threshold

New disk module options:
* threshold_type: ^(percentage|[kmgt]?bytes)_(free|avail)$
* low_threshold: <double>

fixes #912
For the %percentage display of batteries, drop the leading '0' for values < 10.
Unify use of string comparisons

* strncmp(s1, s2, strlen(s2)) → BEGINS_WITH(s1, s2)
* strncmp(s1, s2, strlen(s1)) → strcmp(s1, s2)
* Prefer case-insensitive comparison for options
Remove custom color options from order array
Avoid unnecessary string duplication

This patch removes an unnecessary string duplication that was only
used to avoid a compiler warning.
Implement battery functionality for NetBSD users

This patch takes a similar approach as the NetBSD CPU temperature
code in that it uses proplib(3) to walk dictionaries supplied by
envsys(4).

In addition to providing the basic functionality, it:

* Provides all existing format specifiers (%emptytime %consumption
  %status %percentage %remaining)
* Respects all existing config options (hide_seconds, low_threshold,
  integer_battery_capacity, last_full_capacity)
* Projects "time until full" when battery status is CS_CHARGING
Fix NetBSD CPU temp gauge bug

This patch fixes a bug in which multiple (conflicting) CPU temps may be
included in the output for the "cpu temperature" module.

The bug is due to the way that the code parsed the envsys(4)-returned data,
and would manifest itself on x86-based NetBSD machines, since those use
cputemp(4) as well as acpitz(4), thereby creating multiple envsys(4) entries
with identical descriptions but which refer to different physical sensors.

Instead of matching the description attribute of each device returned by
envsys(4) against the target format, this patch throws away non-matching keys
in the first instruction inside the dict walk. This has the benefit of sparing
unnecessary CPU cycles, and preventing other sensors from being included
erroneously.

Additionally, the THERMAL_ZONE format is now joined with OpenBSD in that it
uses acpitz(4) explicitly. This is prefered since it is much older (dating
back to NetBSD 2.0), and does not exclude x86-based users (as with cputemp(4)).
run_watch: check all matching pid files (until first valid one) (Thanks brotbart)

fixes #1245
add mpd implementation