Issue 253: Fix linting

[dogle-scottlogic]

Fix the linting, addressed issue #253 :

• Update path matching to match all posts correctly
• Remove author from category (Note: this seems to be something siteleaf adds so might need to look at that)
• Allow up to 3 categories to be specified
• Make 130 char summary a soft (WARN) min
• Fix unknown category issues

[dogle-scottlogic]

As far as I can see the accessibility job is failing due to the number of files changed - although the feedback isn't super helpful

[chriswilty]

There are a lot of whitespace changes, moving summary lines onto a single line. Surely it's not the linter does that? It is making this PR far larger than it needs to be.

Also, I'm not convinced Siteleaf adds author as category, as my first post from 9th May was done in siteleaf and is not in the change list.

[dogle-scottlogic]

This was a side effect of the method I used to remove the author. I've tried a different approach which seems to preserve the formatting of other fields

[chriswilty]

I've not checked every single file, but I have noted that most are single-line removals which makes sens. The linter script also seems fine.

Don't worry about the pa11y error, we're not changing any actual post content so can ignore it.