lnav v0.8.1 released!

After way too long, lnav v0.8.1 has been released.  Here is a rundown of the changes:

Features:
     * Added a spectrogram command and view that displays the values of a
       numeric field over time.  The view works for log message fields or
       for database result columns.
     * Log formats can now create SQL views and execute other statements
       by adding '.sql' files to their format directories.  The SQL scripts
       will be executed on startup.
     * Added 'json_group_object' and 'json_group_array' aggregate SQL
       functions that collects values from a GROUP BY query into a JSON
       object or array, respectively.
     * The SQL view will now graph values found in JSON objects/arrays in
       addition to the regular columns in the result.
     * Added an 'regexp_match(<re>, <str>)' SQL function that can be used to
       extract values from a string using a regular expression.
     * Added an 'extract(<str>)' SQL function that extracts values using the
       same data discover/extraction parser used in the 'logline' table.
     * Added a "summary" overlay line to the bottom of the log view that
       displays how long ago the last message was received, along with the
       total number of files and the error rate over the past five minutes.
     * Pressing 'V' in the DB view will now check for a column with a
       timestamp and move to the corresponding time in the log view.
     * Added 'a/A' hotkeys to restore a view previously popped with 'q/Q'.
     * Added ":hide-lines-before", ":hide-lines-after", and
       ":show-lines-before-and-after" commands so that you can filter out
       log lines based on time.
     * Scripts containing lnav commands/queries can now be executed using
       the pipe ('|') hotkey.  See the documentation for more information.
     * Added an ":eval" command that can be used to execute a command or
       query after performing environment variable substitution.
     * Added an ":echo" command that can be useful for scripts to message
       the user.
     * The "log_part" column can now be set with an SQL UPDATE statement.
     * Added a "log_body" hidden column that returns the body of the log
       message.
     * Added ":config", ":reset-config", and ":save-config" commands to change
       configuration options, reset to default, and save them for future
       executions.
     * Added a "/ui/clock-format" configuration option that controls the time
       format in the top-left corner.
     * Added a "/ui/dim-text" configuration option that controls the brightness
       of text in the UI.
     * Added support for TAI64 timestamps (http://cr.yp.to/libtai/tai64.html).
     * Added a safe execution mode. If the 'LNAVSECURE' environment variable is
       set before executing lnav, the following commands are disabled:
       - open
       - pipe-to
       - pipe-line-to
       - write-*-to
       This makes it easier to run lnav with escalated privileges in restricted
       environments, without the risk of users being able to use the above
       mentioned commands to gain privileged access.

     Interface Changes:
     * The 'o/O' hotkeys have been reassigned to navigate through log
       messages that have a matching "opid" field.  The old action of
       moving forward and backward by 60 minutes can be simulated by
       using the ':goto' command with a relative time and the 'r/R'
       hotkeys.
     * Log messages with timestamps that pre-date previous log messages will
       have the timestamp highlighted in yellow and underlined.  These out-
       of-time-order messages will be assigned the time of the previous
       message for sorting purposes.  You can press the 'p' hotkey to examine
       the 'Received Time' of the message as well as the time parsed from the
       original message.  A "log_actual_time" hidden field has also been
       added to the SQLite virtual table so you can operate on the original
       message time from the file.
     * The 'A/B' hotkeys for moving forward/backward by 10% line increments
       have been reassigned to '[' and ']'.  The 'a' and 'A' hotkeys are now
       used to return to the previously popped view while trying to preserve
       the time range.  For example, after leaving the spectrogram view with
       'q', you can press 'A' return to the view with the top time in the
       spectrogram matching the top time in the log view.
     * The 'Q' hotkey now pops the current view off of the stack while
       maintaining the top time between views.

     Fixes:
     * Issues with tailing JSON logs have been fixed.
     * The jget() SQL function should now work for objects nested in arrays.