Putting examples on matplotlib module

[joaocarvoli]

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• I have read the CONTRIBUTING document.
• My code follows the code style of this project (see .code-style.md).
• All new and existing tests passed (see .testing.md).
• I have added tests to cover my changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly (see .documentation.md).

Description

• What is the current behavior? (You can also link to an open issue here)
  In this pull, I added examples of each function in the matplotlib module.