Finalize support for EditorConfig specification 0.17.2 #46

Although ecformat itself is no EditorConfig core
(ec4rs is the core in use), add the version of the implementation
EditorConfig specification as requested for cores in the specification.
https://spec.editorconfig.org/#versioning 

To show how the string can be used in a more structored and typed way
and to ensure that the string always contains a valid version.
The alternative approach to use macro which returns a semver::Version
seems to be not usable to convert this to string for usage in the
version text of ecformat.

To reduce IO on the disc and speed up the process.

This reverts commit 4177b0fcdd.
Testing the performance difference on the source code of chromium and android
(some larger projects with an EditorConfig)
shows that the previous approach to read the files multiple times is faster
than reading them only ones.
Tests with &str instead of &[u8] to pass the file contents is faster,
but still slower than reading multiple times.
The &[u8] approach takes about 4 to 10 times longer than multiple reads.
The &str approach takes about 1.5 to 2 times longer than multiple reads.
Reason could be a different caching behavior.

There could be .editorconfig files in the parent directories of the
temporary test directories. Adding root = true avoid failing tests due
to this and may also speed up the test runs as less seach for relevant
.editorconfig files is necessary.

Workflow for the docs.rs lint fails as the semver crate is only a
development dependency of ecformat. As ecformat only needs the crate
for the docs test below, adding it as a normal dependency only for
docs.rs is not suitable. Therefore, use a normal web link.