Start of re-structuring of how usage is maintained and reported for the
bank balance system: use SlurmDBD values instead of local *_usage files.

Old system:
- read usage information from local *_usage files via 'sshare'
- PriorityDecayHalfLife must be disabled, with PriorityUsageResetPeriod=NONE

New system:
- read usage information from SlurmDBD via 'sreport'
- DecayHalfLife can be re-enabled

The new system could well be slower in practice, because you're contacting the
remote SlurmDBD, instead of just reading from local files.

New feature: "-U username" option to check a given user's balance.

TODO: update docs to reflect changes
add new flag to parent script
updated test from sshare to sreport
update docs to reflect change from sshare to sreport
Bumped version number to 1.3.1
start ChangeLog file
move the print statements to function calls
compact the width of the balance print a little
missing usage info for new '-U user' parameter
add an '-s yyyy-mm-dd' param to specify the start date for the report; update docs with this option
Bumped version number to 1.3.1
Bumped version number to 1.3.2
Bumped version number to 1.3.2