Add keyword arguments to spectrogram (v923z#657)

* re-work spectrogram method, so that RAM can be re-used

* update docs with spectrogram changes

fix loadtxt for the case, when built-in complexes are not supported (v…

…923z#666)

ndarray_from_mp_obj correctly treats Booleans (v923z#613)

fix how arctan2 treats scalars (v923z#546)

Merge pull request v923z#456 from v923z/complex2

Complex2

Merge pull request v923z#458 from v923z/sum-fix

Sum fix

Merge pull request v923z#453 from RobertoRoos/release/v1.7

Adding branch release/v1.7 to suit version 1.7.9

Merge pull request v923z#452 from RobertoRoos/release/v0.54

Adding branch release/v0.54 to suit version 0.54.6

Merge pull request v923z#451 from RobertoRoos/release/v0.36

Adding branch release/v0.36 to suit version 0.36.1

Merge pull request v923z#428 from v923z/fix-4d

fix sum for 4D arrays