Byte compilation warnings

[jcs090218]

feature-mode.el:101:2: Warning: custom-declare-variable
    `feature-enable-back-denting' docstring wider than 80 characters

In given-when-then-wordlength:
feature-mode.el:372:14: Warning: ‘some’ is an obsolete function (as of 27.1);
    use ‘cl-some’ instead.

In compute-given-when-then-offset:
feature-mode.el:380:15: Warning: assignment to free variable
    ‘current-word-length’
feature-mode.el:384:17: Warning: reference to free variable
    ‘current-word-length’
feature-mode.el:391:35: Warning: assignment to free variable
    ‘search-word-length’
feature-mode.el:393:37: Warning: reference to free variable
    ‘search-word-length’
feature-mode.el:394:67: Warning: reference to free variable ‘search’
feature-mode.el:395:21: Warning: assignment to free variable
    ‘previous-lengths’
feature-mode.el:397:30: Warning: reference to free variable ‘previous-lengths’
feature-mode.el:619:4: Warning: ‘yas/load-directory’ is an obsolete function
    (as of yasnippet 0.8); use ‘yas-load-directory’ instead.

In feature-verify-scenario-at-pos:
feature-mode.el:629:2: Warning: docstring wider than 80 characters
feature-mode.el:683:2: Warning: ‘defun*’ is an obsolete alias (as of 27.1);
    use ‘cl-defun’ instead.

In feature-project-root:
feature-mode.el:710:2: Warning: docstring wider than 80 characters

In end of data:
feature-mode.el:703:12: Warning: the function ‘chruby-use-corresponding’ is
    not known to be defined.
feature-mode.el:701:12: Warning: the function
    ‘rvm-activate-corresponding-ruby’ is not known to be defined.
feature-mode.el:576:4: Warning: the function ‘turn-on-orgtbl’ is not known to
    be defined.

[michaelklishin]

You are welcome to submit a PR that fixes the warnings.

[jcs090218]

PR in #95.