migrate PyArray contructors to Bound API (Part 2)

[Icxolu]

Following #416

This continues the migration of PyArray constructors to the Bound API. This migrates with PyArray::{from_slice, arange}.

[adamreichold]

Some doctests seem to fail to compile. You check the doc build using ./x.py d.

Please also have a look whether the benchmarks need adjustments. They are included in the default ./x.py action.

[Icxolu]

Please also have a look whether the benchmarks need adjustments. They are included in the default ./x.py action.

Sure, I'll check again once #417 is merged

[Icxolu]

Rebased and updated benchmarks. For reference: The deprecation warnings in the benchmarks did not show up on ./x.py for me

[adamreichold]

The deprecation warnings in the benchmarks did not show up on ./x.py for me

Ah yes, the script checks if a nightly toolchain is used and builds the benchmarks only in this case (as they require std's unstable test feature).