First draft of "Deploying to Heroku Cloud" cookbook article
Fixed som RST syntax errors
Added the new cookbook to the article map
Fixed all problems reported by @WouterJ
Fixed the target of one link
Applied all the fixes suggested by @xabbuh
feature #4045 Added a new "Deploying to Heroku Cloud" cookbook article (javiereguiluz)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #4045).

Discussion
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Added a new "Deploying to Heroku Cloud" cookbook article

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | master
| Fixed tickets | -

Commits
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0a1ba36 Applied all the fixes suggested by @xabbuh
87c0d08 Fixed the target of one link
2fdfd6d Fixed all problems reported by @WouterJ
31003b2 Added the new cookbook to the article map
d76bf8e Fixed som RST syntax errors
0371402 First draft of "Deploying to Heroku Cloud" cookbook article
Merge branch '2.3' into 2.4

* 2.3:
  Applied all the fixes suggested by @xabbuh
  Fixed the target of one link
  Fixed all problems reported by @WouterJ
  Added the new cookbook to the article map
  Fixed som RST syntax errors
  First draft of "Deploying to Heroku Cloud" cookbook article