Omit YAML document start marker for single-document output

Single-document YAML output no longer includes a leading `---` marker
by default, aligning with standard YAML conventions. Multi-document
files still emit the marker for each document. A new
`--enforce-document-start-marker` flag is added to opt back into
always printing the marker.

Signed-off-by: Matthias Diester <mddiester@gmail.com>

Bump `github.com/gonvenience/ytbx` to `v1.5.0`

Bump `github.com/gonvenience/ytbx` to `v1.5.0`.

Fix test case that now has a changed order.

Signed-off-by: Matthias Diester <mddiester@gmail.com>

Add test case for empty document not being read correctly

Ref: #16

Bump `ytbx` to get fix for empty document parsing issue.

Fix incorrect diff for mixing types in a list

Bump `neat` to include fix for quoting numbers.

Include scalar tag in hash calculation to differentiate between types.

Simplify variables declarations.

Move `createLookUpMap` function into `simpleLists` to avoid unnecessary
method on `compare`, since it's only used in one function.

Fix grab issue with non-standard identifier

Code detected a non-standard identifier for a named entry list. The non-
standard identifier contained dots and slashes in its name. Using grab
function interpreted the dots as path separators and not as text and
therefore tried to search the structure, which failed.

Replace grab with simple mapping context key/value search, since in this
use case it is safe to assume that it's a mapping context with keys and
values an no deep structure.

Simplified some variable declarations.

Refactor flag usage and defaults

Rename newly introduced marshal flag to `--format-strings`.

Introduce flag grouping to improve help/usage documentation.

Refactor report preferences into struct with defaults to have
settings and defaults in one place.

Add missing test case for string formatting.

Refactor new formatting code to only follow through if both
from and to value can be formatted.

Removed `min` function to use built-in version.

refactor: extract Colorizer interface for pluggable diff coloring

Introduce an exported `Colorizer` interface that encapsulates all color
operations used by the human-readable diff output. `HumanReport` gets a
`Colorizer` field that defaults to `BuntColorizer` (preserving existing
behavior) when nil.

This allows downstream consumers to swap in alternative coloring backends
(e.g. `mgutz/ansi`) without forking, by implementing the interface and
setting `report.Colorizer`.

Changes:
- `colors.go`: define `Colorizer` interface (15 methods) and
  `BuntColorizer` as the default implementation
- `output.go`: deleted, YAML color functions moved to `BuntColorizer`
- `output_human.go`: thread colorizer through `HumanReport`, convert
  `highlightRemovals`, `highlightAdditions`, and
  `showWhitespaceCharacters` to receiver methods

Unify Go YAML import names.

Unify Go YAML import names.

Signed-off-by: Matthias Diester <matthias.diester@de.ibm.com>

docs(README): add mise alternative method installation

Signed-off-by: jylenhof <jygithub@lenhof.eu.org>

Merge pull request #521 from homeport/fix/indent-flag

Fix new `--use-indent-lines` wiring in code