Paleozoic Era

• allow jagged arrays of covariance keys
• simplify

Phanerozoic Eon

• Fixes #5 value error if covariance keys have multiple observations
• fixes scaling covariance cross terms in addition to diagonals

Neoproterozoic Era

• Fixes #4, ValueError if just one observation

Mesoproterozoic Era

• fixes #2: figure out nobs automatically
• fixes #3: sparse matrices
• adds multiprocessing pool
• uses pvlib instead of proprietary solar utils
• travis build

Paleoproterozoic Era

• Fixes #1 works with Pint's @ureg.wraps() now
• use indices for positional args - don't use inspect.argspec
• test Jacobian estimates using AlgoPy and numdifftools
• update docs with more examples, show Jacobian erros vs AlgoPy

Proterozoic Eon

• specify covariance keys, group args and returns
• covariance is dimensionless fraction
• more complex examples, test with Python extension and with multiple
  input arguments and returns

Archean Eon

• Fix nargs and nf order mixup in Jacobian
• add more complex test
• fix tile cov by nobs
• move partial derivative to subfunction
• try threading, but same speed, and would only work with NumPy anyway
• TODO: try pthreads or winthreads if safe to release Python GIL

Hadean Eon

• adds covariance to output
• allows __covariance__ to be passed as input
• uses estimate Jacobian based on central finite difference method