First line should summary why this commit was necessary

[baby-gnu]

Hello.

Doing some Git log archeology quite often, I always struggle to find why a commit was done rather than what it does:

• a first line to summary why this commit was done
• a longer description to make explicit the context of the why given in the first line. This description summary how things were done.
• if necessary, a list of files with a summary of what was wrong specifically to this file and the tricky parts

This way:

• git log --oneline master shows why pull requests where accepted
• git show aaafffeee shows what is done by a commit

So, instead of:

Use InventoryBackendPool to retrieve inventory backend

I think it's better to have

`Inventory` is slow and heavy for the backend

We call the backend several times and `Inventory` open and close a connection
at each call which is slow to execute and add load to the backend to open
connections and authenticate them.

We switch the part `Foo` of the software to `InventoryBackendPool` 
which open once a connection pool with the backend and maintain them open
and reopen them if they close unexpectidly.

Ref: #42

Regards.