* Add nodelet implementation.

Add additional nodelet layer to mirror the node
implementation. This allows the Slam GMapping
library to be run as a nodelet instead. This
would allow you to, for example, run it under
the same nodelet manager as the nodelet producing
the /scan output for greater efficiency.

* Remove superfluous semicolons

Removed superfluous semicolons and
mildly clarified info stream output.

* fix comment, change type from double to int

* fix comment, iterations param is not double but int

make sure the laser sent to gmapping is always centered

This reverts commit b1f4ea15.

This reverts commit 46c66d23.

This reverts commit e842d49c.

This is a proper fix + test to #32

This reverts commit dd446726.

Some fixes and tweaks

Example usage:
    ros run gmapping slam_gmapping_replay --scan_topic=/scan --bag_filename=/tmp/in.bag --on_done "rosrun map_server map_saver -f foo" _particles:=100 _maxUrange:=10

Silently discard scans at startup that arrive prior to the TF frames
required by those scans.

TF can't interpolate from non-existant data, so discard scans that
arrive with timestamps prior to the first TF frame.  We do this
expediently by discarding laser scans that throw
ExtrapolationException's until/unless we successfully process our first
scan.

Similarly, ignore LookupException's at startup.

Fix indexing error for inverting scan.

Feature replay on rosbag

removing pointer for Gmapping object

The aim is to provide a way to get exactly the same map after running
gmapping multiple times on the same rosbag file. It wasn't possible with the
tool 'rosbag play', indeed one missing laser scan could provide really
different results.

Moreover, this modification allow to process rosbag offline at the maximum
speed with the guarantee that all lasers scans are processed. It is
 useful in automatic tests and when finding optimal gmapping parameters with a script.

Example usage:
    rosrun gmapping slam_gmapping_replay --scan_topic=/scan --bag_filename=/tmp/in.bag _particles:=100 _maxUrange:=10

more options:
    rosrun gmapping slam_gmapping_replay --help

The objective is to allow future handling of replay offline rosbag files.
This commit also add a variable for the seed, with the objective is to allow to
have repeateable run (for future offline rosbag replay)

Added check that scan goes from -x to x