This updates the test infrastructure to store a git hash of the reference
code, instead of generated .h5 files.  The test infrastructure creates a
cache of the reference .h5 files from the specified git hash if it doesn't
already exist, and then compares against that cache.

This gets rid of the need for git-lfs and the cached .h5 files, requiring
instead the code is checked out from git.

Use overlaid dashes for the head traces.

Also do comparison in preferred IFO order.

These changes improve the modeling of suspensions that have a
temperature gradient along the fibers.  Each stage is split into an
upper and a lower joint, which can have different material properties
assigned in the ifo structure.  The temperature of a joint is that of
the mass to which it is attached.  (However, temperature gradients are
not yet supported within the top or bottom stages.)  The average of
the upper and lower joint dissipation is used to compute the noise.

no functional change, just limits individual function imports to non-array
operations.

Removed normalization of sinc_sqr in dhdl because it is one at DC. Previously the normalization was set by the first frequency point, which is wrong if only high frequencies are considered

Use more generic collections.abc.Mapping to detect a nested dict.

since it's not needed for most operations

implement as __main__ for `gwinc.ifo`

also add to CI.  closes #48

This allows for specifying an order that makes sense without too much loss
of ease of expandability (just need to add an entry to a list).

This finally gets rid of the whole precompIFO function.  It does this
by breaking up precomp into various smaller functions, moving them
into the common IFO noise definition module, and using them
appropriately when needed.  This does result in some of the functions
being called multiple times in the full budget calculation for the
aLIGO-like budgets, but the cost should be minor given the convenience
of getting rid of the whole precomp thing, thereby opening up
everything to non-aLIGO-like configurations.

Even though some functions are calculated multiple times, we're still
orders of magnitude faster than matgwinc, so...  Should still revisit
down the line though.

closes #40

Define new Strain(nb.Calibration) and apply it to all canonical ifo budgets.

Also supports a Budget.calibrations attribute that lists calibrations to be
applied to all noises.

Allows for specifying as a class attribute.

NO FUNCTIONAL CHANGE

residual_gas_cavity() function updated to calculate residual gas noise of
a single evacuated cavity.

ifo ExcessGas Noise class modified to handle specific case
of Fabry-Perot Michelson.

Simplify newtonian noise calculations to return displacement noise for
simplified configuration: either single test mass or single arm.

new suspension_thermal() function for calculating thermal noise of a
single suspended optic.

ifo SuspensionThermal Noise class modified to handle specific case of
Fabry-Perot Michelson.

substrate_thermoelastic() function updated to calculate thermal noise
of a single suspended optic.

ifo SubstrateThermoElastic Noise class modified to handle specific
case of Fabry-Perot Michelson.

substrate_brownian() function updated to calculate thermal noise of a
single suspended optic.

ifo SubstrateBrownian Noise class modified to handle specific case of
Fabry-Perot Michelson.

substrate_thermorefractive() function updated to calculate thermal
noise of a single suspended optic.

ifo ITMThermoRefractive Noise class modified to handle specific case
of Fabry-Perot Michelson.

substrate_carrierdensity() function updated to calculate thermal noise
of a single suspended optic.

ifo ITMCarrierDensity Noise class modified to handle specific case of
Fabry-Perot Michelson.