"Modernize" codebase

[Baptouuuu]

Need

As mentioned in #257 an upgrade of the codebase is interesting in order to type everything to help future upgrades.

Implementation

The following changes have been applied:

• add the : void return type on all methods/functions that return nothing
• add : int return type for Command::execute() as Symfony was moving to enforce developers to return an exit code
• add all primitive types wherever possible (exceptions are for mixed or union types)
• add vimeo/psalm as a dev requirement, configured on the strictest level
• fixed all errors raised by psalm, mainly to provide type hints for command inputs and array templates
• vendor/bin/psalm is now run in travis after phpunit
• replace class strings with the FQCN::class pseudo constant, so tools and IDEs can better understand them
• removed all docblocks that didn't provide information not already provided by the types
• fixed an outdated php version in the preview command (as 7.1 il already enforced in composer.json

Comments

• Since I added : void to the interface Step::__invoke it would require a new major release as it's a BC break. Depending on your release strategy this change may be rollbacked.
• Since the PR changes quite a lot of code I suggest to review commit per commit
• I suggest to replace, in another PR, Travis by GitHub actions. The benefits would be:
  • allow a better test matrix (os(linux, macOs), php(7.1, 7.2, 7.3, 7.4) and dependencies(lowest, normal))
  • split the website deploy job in it's own job (instead of an after success)
  • the split would allow to simplify the code of the travis-auto-deploy command

[Baptouuuu]

I had to specify this bugfix version as it is the minimum required by vimeo/psalm

[Baptouuuu]

Here we type with Twig_Environment but in the documentation of this feature you use Twig\Environment, should I replace Twig_Environment by the namespaced class name ? (There shouldn't be a difference since it's an alias, but I'm not sure of potential side effects)

[mnapoli]

Honestly go the way you prefer, I don't there should be side effects either.

[Baptouuuu]

Since the composer.json refers twig ~1.10 the namespace isn't provided in this version, I'll change the documentation

[mnapoli]

That is awesome! I added a minor comment and then we're good to merge!

Thanks!

[mnapoli]

That isSupported() is for checking that PHP >= 5.4 because that's the version they added the built-in webserver.

We could completely remove that check now instead of upgrading the error message.

[Baptouuuu]

Done

[alanpoulain]

Why not declaring strict typehint to all the files too?

[Baptouuuu]

As suggested by @alanpoulain I added strict types everywhere

[mnapoli]

Awesome thanks!