Implement squeeze and reshape.

[1uc]

These methods allow reshaping the memory space. This can be used as
an alternative to broadcasting.

Example:

Let dset be a dataset with shape [3, 1, 1]. Then,

dset.reshapeMemSpace({3}).read<std::vector<double>>();
dset.squeezeMemSpace({1, 2}).read<std::vector<double>>();

can be used to read into a one-dimensional dataset.

[1uc]

This is preparatory work to allow #992.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.75000% with 13 lines in your changes are missing coverage. Please review.

Project coverage is 86.26%. Comparing base (070badf) to head (1f09187).
Report is 1 commits behind head on master.

Files	Patch %	Lines
src/examples/broadcasting_arrays.cpp	0.00%	9 Missing ⚠️
include/highfive/bits/H5Attribute_misc.hpp	72.72%	3 Missing ⚠️
include/highfive/bits/H5Slice_traits_misc.hpp	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #991      +/-   ##
==========================================
- Coverage   86.31%   86.26%   -0.05%     
==========================================
  Files          92       94       +2     
  Lines        5919     5986      +67     
==========================================
+ Hits         5109     5164      +55     
- Misses        810      822      +12     

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[matz-e]

LGTM