Remove obsolete function calls

In Emacs 29.1 the `point-at-bol` and `point-at-eol` functions are
obsolete. This removes the following warnings when compiling the file:

    In dockerfile-indent-line-function:
    dockerfile-mode.el:159:41: Warning: ‘point-at-bol’ is an obsolete function (as
        of 29.1); use ‘line-beginning-position’ or ‘pos-bol’ instead.
    dockerfile-mode.el:163:37: Warning: ‘point-at-eol’ is an obsolete function (as
        of 29.1); use ‘line-end-position’ or ‘pos-eol’ instead.
    dockerfile-mode.el:164:32: Warning: ‘point-at-eol’ is an obsolete function (as
        of 29.1); use ‘line-end-position’ or ‘pos-eol’ instead.
    dockerfile-mode.el:166:27: Warning: ‘point-at-bol’ is an obsolete function (as
        of 29.1); use ‘line-beginning-position’ or ‘pos-bol’ instead.

It is safe to use these new functions as they were introduced as of
Emacs 20.

Fix: remove repeated switch in docstring

updating build string example

Add --pull and --force-rm switches toggling defcustoms.

Added version and URL header

fix: false positives caused by auto-mode-alist pattern

The old pattern would match the following filenames:

- *Dockerfile
- *Dockerfile.*

This is because the pattern does not start with a slash indicating the
beginning of the basename. Personally this led to a few false positives,
like for example "siren-dockerfile.el" that sets up and configures
dockerfile-mode in my Emacs configuration.

This change restricts the patterns to:

- Dockerfile
- Dockerfile.*
- *.dockerfile

I believe this is still wide enough to capture all common naming
conventions for Dockerfiles.

Remove keybinding to #'dockerfile-test-function

Merge pull request #19 from giuseppe/giuseppe/color-label

dockerfile-mode.el: add LABEL to the list of known keywords

Merge pull request #10 from j0ni/accommodate-ethan-wspace

Correctly set require-final-newline

Added copy and onbuild commands