ENH: expanded data range

[jklenzing]

Is your feature request related to a problem? Please describe.
The current data range of available orbits is three years based on inheritance from pysat.

Describe the solution you'd like
Tie to the start and stop dates to 1957 to 2056, the operational range of TLEs.

Describe alternatives you've considered
The runtime does increase when carrying around a longer list of files. As a test, changing from a three-year range to a hundred-year range increases the run time about 40% (from 0.47s to 0.64s per orbit on average, running >100 orbits randomly). In theory we could also pass through file_date_range as an optional argument for a quicker version of this, but may still run into an overhead issue.

Additional context
The list of fake files is required by pysat, ie, a file must exist before it can be loaded.

See #66 for more discussion.

[jklenzing]

Currently the code mirrors the pysat test instruments in that it creates a date range of three years around the nominal test date. I can hardwire a file_date_range into the instrument, but this prevents me from passing through the alternate file_date_range as a kwarg when initializing the instrument.

[jklenzing]

Adding a question label since this may be dropped. Adding a custom file_date_range has been sufficient in current analysis, but needs may change down the line.

[jklenzing]

Should make a design decision by 0.4.0 release.