Add features to fextract

[mic84]

Summary

Add the following features to fextract:

• user option to set the number of decimals in the output of reals
• user option to set a cut-off tolerance: anything smaller than the tolerance gets printed as zero
• user option to disable the job summary report at the end of the output

Additional background

The job summary report is disabled by default in contrast with the current behaviour.

Checklist

The proposed changes:

• fix a bug or incorrect behavior in AMReX
• add new capabilities to AMReX
• changes answers in the test suite to more than roundoff level
• are likely to significantly affect the results of downstream AMReX users
• are described in the proposed changes to the AMReX documentation, if appropriate