Fixed Negative capturedVideoSeconds Bug

In PBJVision.m, I added an if statement to handle situations where the method capturedVideoSeconds was returning a negative value.
This situation had prevented my multi-view application from recognizing that new video was being captured on a return visit to a view that recorded video.
Merge pull request #123 from zodio/master

Check if DLog is defined before defining it to avoid warnings/conflicts
PBJVision, ensure we're not adding nil pointers
PBJVision, remove restore format
remove duration from new offset buffer
PBJVision, minor cleanup, moved a method
PBJVision, added maximumCaptureDuration property
 - delegate callback will be triggered when maximum is met or exceeded
Merge pull request #122 from eliotw1/fix-video-timestamp-error

Fixed Negative capturedVideoSeconds Bug
add a comment
add a method for determining focus POI support
move two methods
PBJVision, rename methods to ensure adoption of :

- (void)focusExposeAndAdjustWhiteBalanceAtAdjustedPoint:(CGPoint)adjustedPoint;
PBJMediaWriter, disable logging in debug builds
PBJVision, add a video profile level to the compression settings
Update README.md
PBJMediaWriter, change default format to MPEG4, fixes GH-131
add a travis-ci config file
Project file, remove dead target reference
updated README
Update README.md