Add empty host and leading slash to Windows file paths

[phil-davis]

1. add an explicit unit test for issue Windows file prefix #31
2. Adjust README to mention Windows-style paths
3. Add empty host and leading slash to Windows file paths (this is a remake of PR Add empty host and trailing slash to windows file paths #71
4. changelog and version bump to 3.0.0

[codecov]

Codecov Report

Merging #82 (df6803e) into master (50c2f98) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #82      +/-   ##
==========================================
+ Coverage   98.49%   98.54%   +0.04%     
==========================================
  Files           1        1              
  Lines         133      137       +4     
==========================================
+ Hits          131      135       +4     
  Misses          2        2              

Impacted Files	Coverage Δ
lib/functions.php	98.54% <100.00%> (+0.04%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[phil-davis]

Wait until we decide the final actions to resolve issue #81 because maybe the text here will only apply to the next major release.

[phil-davis]

I will finish this tomorrow - give people a few hours to point out any errors I might have made in the releases 2.2.4 and 2.3.2

[phil-davis]

A week has passed - let's get moving again!

[staabm]

all good - thanks for working on it phil!