Add study case with MMM + CLV

[ricardoV94]

Create some fake dataset with continuous non-contractual process and build a story around:

1. Using MMM to infer cost of acquisition across different channels
2. Using CLV to infer differential lifetime value of customers coming from different channels
3. Making business decision that takes the two sources of information into account
   a. Preferring to invest in a channel with higher CAC because of higher CLV
   b. Binary decision to not further invest in channel if CLV is lower than CAC

Requires: #24, #19, #39

We might use this case-study for the initial announcement of the package

[ColtAllen]

I could also see RFM Segmentation being valuable for this, because customers in different segments would benefit from different strategies, which can be tied back directly to marketing budgets and channel contributions.