Tweaked progress bar animation
minor #17 Tweaked progress bar animation (1ed)

This PR was merged into the 1.0-dev branch.

Discussion
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Tweaked progress bar animation

Before:
![before](https://cloud.githubusercontent.com/assets/162986/4667182/5c288312-555a-11e4-848f-ffd6e278a18c.gif)

After:
![after](https://cloud.githubusercontent.com/assets/162986/4667184/600e8986-555a-11e4-89aa-e7ea9a62781e.gif)

I know it's subjective but I think the second one looks better. Tested on Ubuntu 14.04.

Commits
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ad899c8 Tweaked progress bar animation
Added a complete Symfony version checker to decide if we can install it
feature #29 Added a complete Symfony version checker to decide if we can install it (javiereguiluz)

This PR was squashed before being merged into the 1.0-dev branch (closes #29).

Discussion
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Added a complete Symfony version checker to decide if we can install it

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #25
| License       | MIT
| Doc PR        | -

Commits
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6b323fc Added a complete Symfony version checker to decide if we can install it
improve error message for PHP < 5.4

When the user uses a PHP version smaller than 5.4, they are not able
to use the Symfony Installer. Instead, they are presented a nice error
message telling them to use the `composer create-project` command
instead. However, if that command is executed without a version
number, the user will get the latest stable release of the Symfony
Standard Edition. Especially when the user passed a custom version
number to the Symfony Installer, this might not be the desired
version. Therefore, it is reasonable to pass the required version
number to Composer.