LogC version 0.2.0

Added
* Details about compilation and testing to README.adoc
* Output format fragment `LOG_FP_LEVEL_NAME`
* Output format field `%|` that is handled as "else" inside conditions
* Support for output level offset
* Function `log_offset_level` to set level relative to current setting
* Support for output to syslog
* New log creation helper macro `DAEMON_LOG` for applications commonly
  started in background
* `--log-file` argp option
* `--log-level` argp otion

Changed
* Log macros for specific log prefixed with `log_`
* Log macros using `DEFLOG` renamed from upper-case to lower-case
* Macro `log` was renamed to `logc` to not collide with `math.h`'s `log`
* Function `_log` was renamed to `_logc` to be consistent with `log`
  rename
* Code is now compiled explicitly with C11 standard support
* Output format not-empty condition do not investigate sub-conditions,
  instead it considers them non-empty if they condition is fulfilled.
* Default formats now use `LOG_FP_LEVEL_NAME` for message type
  representation
* How message level and log level is mixed and because of that most of
  the function now take `int` instead of `enum log_level`
* Environment variable `LOG_LEVEL` is now expected to be number and not
  string
* Message level enum renamed from `log_level` to `log_message_level` and
  values are shifted partially to negative
* `ASSERT` renamed to `assert` and `assert` to `log_assert` in
  `logc_assert.h`
* Utility macro `std_fatal` now provide result from statement

Removed
* Output format fields `%l` and `%L`

Fixed
* Linter and tests inclusion when they were not enabled by configuration
  script