Automatic path discovery and some code clean up

[ldes89150]

Hi,

Thanks for creating this amazing library!! This saves us a lot of time on development! I made a few changes to the code. Hope they will be useful.

• New Feature: Automatically discover the ALP lib path (d8a7f2c2994e4e6a9ed0385b1a2308e9143218a0)
• Best Practice: Using "is" while comparing with None (PEP 8 preferred approach) (47daac28deb1f6877d4683f7e4934c3e5e707c0a)
• Replace obsolete error raising function (fdb3df61c4cf3a75eb59a584d8d2ae7a62957e94 bc65a0f99f4eed7be7086c6849c97193ee368a12)
• Best Practice: Raise an ALPError instead of general Exception (19f4e8f0f193a3eb3dba2dce808413cd384b27f4)
• Fix mixed indentation of tabs and whitespaces (eb20345c21ad47b55f0c6db3fa7f8c0e7e10e01e)
• Fix typo (dbf6f305c342f6c1e5f70467906929ed83614a53)
• Doc update: instructions on installation from the source (28b1ae6a8577259365e3f5ed447cc8a66cb70db0)