Resolve "Fix local to global index conversion in test cases"

Closes #85

See merge request !85

Resolve "set_meshSpacing add back to UniformCartesian"

Closes #84

See merge request !84

Resolve "fix Heffte bug"

Closes #82

See merge request !82

Resolve "Use `const` reference for norms"

Closes #81

See merge request !81

Implement inner product

Closes #73

See merge request !74

Add file descriptions and GPL notice

Remove sqrt call for fewer sources of error

Compare values directly with correct values and allow deviation of 1e-6

Convert norm to non-member function

Resolve "Add parameter class"

Closes #75

See merge request !76

Resolve "Cleanup UniformCartesian"

Closes #78

See merge request !79

Resolve "Newer compiler toolchain and C++ standard"

Closes #76

See merge request !77