Add emcee notebook and update parameter bounds

[raoulcollenteur]

This PR add an example of how to use MCMC for Pastas models. To enable this, the parameter bounds are changed a little, notably the following:

• noise_alpha lower bound 0f 1e-5 instead of 0
• Exponential_A lower bound 0f 1e-5 instead of 0
• Gamma_A lower bound 0f 1e-5 instead of 0
• Exponential_a upper bound of 1000 instead of 5000
• Gamma_a upper bound of 1000 instead of 5000

These should not impact anything, as such a low A/alpha and high Gamma_a are very unlikely to happen.

The notebook is not tested because it depends on the corner and emcee packages.

[rubencalje]

Seems ok, but cannot oversee the consequences of changing the parameter bounds.

[raoulcollenteur]

Here is an overview of what got changed by this pull request:

Complexity increasing per file
==============================
- pastas/io/base.py  1
         

Clones removed
==============
+ pastas/rfunc.py  -4
         

See the complete overview on Codacy

[raoulcollenteur]

All good to go.