Fix spelling of continuous globally

[grlee77]

@tayebzaidi pointed out another misspelling of continuous than the one recently resolved in #360. A quick grep of the codebase revealed several other instances.

Fortunately, none of these are in function names in the Python API, so there should not be a backwards compatibility concern for PyWavelets itself. Some function names in the underlying C/Cython code were modified, but I don't believe we make any guarantees regarding backward compatibility of the code in the private _extensions folder?

[codecov-io]

Codecov Report

Merging #362 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #362   +/-   ##
=======================================
  Coverage   83.55%   83.55%           
=======================================
  Files          21       21           
  Lines        3332     3332           
  Branches      567      567           
=======================================
  Hits         2784     2784           
  Misses        484      484           
  Partials       64       64

Impacted Files	Coverage Δ
pywt/_cwt.py	81.25% <ø> (ø)	⬆️
pywt/_extensions/c/wavelets.c	85.74% <100%> (ø)	⬆️
pywt/_extensions/_pywt.pyx	71.48% <100%> (ø)	⬆️

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[rgommers]

Some function names in the underlying C/Cython code were modified, but I don't believe we make any guarantees regarding backward compatibility of the code in the private _extensions folder?

Indeed, fine to change. Thanks @grlee77, merged.