No changes in functionalities in current patch update. Only fixes and additions are made to
follow JOSS guidelines.

letter size paper

Fixes to JOSS code snippets.

Organize source code of the same purpose into a subdirectory. Eg:
```
src/ACWT.jl                     src/ACWT.jl
src/acwt_all.jl         ->      src/acwt/acwt_all.jl
src/acwt_one_level.jl           src/acwt/acwt_one_level.jl
src/acwt_utils.jl               src/acwt/acwt_utils.jl
```

- Update function documentations
- Add `ns_idwt`, `nonstd_wavemult` to be exported from module.

Updates:
- Standard form wavelet multiplication.
- Documentation for `WaveMult` module.

TODO:
- Add examples in `WaveMult` documentations.

- Added parentheses to condition evaluation in `stretchmatrix` function. This improves the
  condition evaluation process that was previously buggy and produces the wrong logical expressions.
- Added a line in `mat2sparseform_nonstd` function. Previous implementation did not produce
  the right answer.

In both `mat2sparse_nonstd` and `mat2sparse_std` functions, the line
```
maxcolnorm = (maximum ∘ mapslices)(norm, Mw, dims = 1)
```
is changed to
```
maxcolnorm = mapslices(norm, Mw, dims = 1) |> maximum
```