add Geometric, Gaussian and Weibull Kernel

[virgile-baudrot]

Description

Additional kernels: Geometric, Gaussian and Weibull Formulation founds in Nathan 2012, "Dispersal kernels: review" from the book Dispersal Ecology and Evolution (2012) and Walker et al. (2019) "A Spatio-Temporal Exposure-Hazard Model for Assessing Biological Risk and Impact"

Changes (choose one only, with x or click after creating PR):

• [x] New formulation/rule
• [ ] Documentation
• [ ] Bug fix for existing rules (non-breaking syntax)
• [ ] Minor change to existing rules (no breaks to old syntax)
• [ ] Major change to existing rules (breaking syntax, needs a breaking version bump)

Checklist:

• [x] My code follows the BlueStyle style guide
• [x] My code is commented with explanations of anything hard to understand
• [x] There are no unnecessary or unrelated code changes included in this PR
• [x] There are no dependencies added: if so, please consider if they are necessary and explain why they are required

For bugfixes

• [ ] My PR addresses a single bug/connected group of bugs
• [ ] I have included a test that will ensure the bug does not reoccur

For new Rules

• [x] My PR is limited to a clear theme/conceptual unit (otherwise make multiple PRs that can be discussed separately).
• [x] New rules have tests in a file of the same name as the rule file, e.g. /test/newrulename.jl
• [ ] I have cited the source of the new formulation/s, if applicable
• [x] I have added a documentation string to formulation struct/s, and added an entry in the docs
• [ ] The doc string has an Example block using jldoctest, like :