Add support for time zone offsets

FlySight normally names files and sets modification times using UTC. This
changeset adds a TZ_Offset configuration value, allowing the user to work
in local time.

The logged data retains the same format, e.g. "2013-09-04T02:02:39.50Z",
regardless of TZ_Offset, but this way a day's worth of skydives will be
stored in the same directory and with filesystem timestamps suitable for
correlating with video files or other captured data.
Added multiplier for chirp step
Changed atoi to strol in Config.c
Use atol instead of strtol
Merge pull request #37 from crwper/fix_config_val_truncation

Changed atoi to atol in Config.c
Cleaned up speech generation and added unit text
Removed speech text filter in UBX_Task
Merge pull request #38 from crwper/fix_chirp

Adjust chirp step to account for tone sample length
More corrections to allow for units in speech
Merge pull request #8 from willglynn/tz_offset

Add support for time zone offsets
Merge pull request #39 from crwper/clean_up_speech_generation

Clean up speech generation
Look for groups of four messages with the same time-of-week instead of looking for messages in a given order
Back to accepting only 3D fixes
Merge pull request #41 from crwper/fix_message_order

Fix message order
Added heading and course accuracy to log output
Merge pull request #40 from crwper/add_heading

Add heading
Split flush into three parts
Remove direct flush when header is written
Merge FatFS changes into flyblind
Merge pull request #2 from crwper/merge_fatfs_changes

Fixed timing issues