[cookbook][doctrine/reverse_engineering] fixed extension prefix for mapping file generated by doctrine:mapping:convert
[cookbook][doctrine/reverse_engineering] fixed output path specification for yml or xml mapping file
[cookbook][doctrine/reverse_engineering] add description to insert namespace
[cookbook][doctrine/reverse_engineering]changed the second command to execute from doctrine:mapping:import to doctrine:mapping:convert
Rewrote download sentence
Book/Form : Adding a new section about defining forms as service

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | all
| Fixed ticket  | -
Clarifying form / form type
Fixing typo
Following @WouterJ recommandations
Minor text fix
Merge pull request #2673 from J7mbo/patch-1

Minor text fix
fixed markup
Fixed formatting

A missing space caused a </code> tag to not close correctly.
Updated to 2.3.0
fixed typo
updated components to 2.3
added example on how to use InputArgument::IS_ARRAY, added overview of all three argument variants
add missing space
removed branch versions
put class constants within double backticks