[TASK] Reformat code for increased readability, match code style rules

[vertexvaar]

There are some code style (especially "soft" line length limit) violations and inline if parts, which leave the code not as readable as it possibly could be. This patch only changes code style, multiple string concatenations and inline if statements.

[helhum]

In general I like this change. However it is pretty hard to review (harder than it could be) because you mix functional changes (changing tenary to if, adding DIRECTORY_SEPARATOR to some local vars, which previously hadn't this) with code style changes.

Could you make two separate pull requests for that? One with whitespace changes only, and one with additional changes (like changing "if" constructs)

Any reasons for the DIRECTORY_SEPARATOR changes? Imho it is better to keep every var containing a path consistently either with or without trailing slash, and to be consistent with composer code (and how PHP handles realpaths), I'd for for without trailing slash.