Hmatrices

[Diff since v0.1.3](https://github.com/WaveProp/HMatrices.jl/compare/v0.1.3...v0.2.0)


**Closed issues:**
- Assembling of Helmholtz kernel (25)

**Merged pull requests:**
- Port code from `WavePropBase` and drop dependency (27) (maltezfaria)
- Bump to 0.2 (28) (maltezfaria)

[Diff since v0.1.2](https://github.com/WaveProp/HMatrices.jl/compare/v0.1.2...v0.1.3)


**Closed issues:**
- The ploting in the example shown in the readme fails. (18)

**Merged pull requests:**
- CompatHelper: bump compat for AbstractTrees to 0.4, (keep existing compat) (19) (github-actions[bot])

[Diff since v0.1.1](https://github.com/WaveProp/HMatrices.jl/compare/v0.1.1...v0.1.2)

Closes 18

[Diff since v0.1.0](https://github.com/WaveProp/HMatrices.jl/compare/v0.1.0...v0.1.1)

**Closed issues:**
- Allow HMatrix of `SMatrix` entries (15)

**Merged pull requests:**
- Lfaria/dev (16) (maltezfaria)