Returns a new string that is a copy of +self+ with certain characters removed;
the removed characters are all instances of those specified by the given string +selectors+.

For one 1-character selector,
removes all instances of that character:

  s = 'abracadabra'
  s.delete('a') # => "brcdbr"
  s.delete('b') # => "aracadara"
  s.delete('x') # => "abracadabra"
  s.delete('')  # => "abracadabra"

  s = 'よろしくお願いします'
  s.delete('よ') # => "ろしくお願いします"
  s.delete('し') # => "よろくお願います"

For one multi-character selector,
removes all instances of the specified characters:

  s = 'abracadabra'
  s.delete('ab')     # => "rcdr"
  s.delete('abc')    # => "rdr"
  s.delete('abcd')   # => "rr"
  s.delete('abcdr')  # => ""
  s.delete('abcdrx') # => ""

Order and repetition do not matter:

  s.delete('ba')   == s.delete('ab') # => true
  s.delete('baab') == s.delete('ab') # => true

For multiple selectors,
forms a single selector that is the intersection of characters in all selectors
and removes all instances of characters specified by that selector:

  s = 'abcdefg'
  s.delete('abcde', 'dcbfg') == s.delete('bcd') # => true
  s.delete('abc', 'def')     == s.delete('')    # => true

In a character selector, three characters get special treatment:

- A caret (<tt>'^'</tt>) functions as a _negation_ operator
  for the immediately following characters:

    s = 'abracadabra'
    s.delete('^bc') # => "bcb"  # Deletes all except 'b' and 'c'.

- A hyphen (<tt>'-'</tt>) between two other characters defines a _range_ of characters:

    s = 'abracadabra'
    s.delete('a-c') # => "rdr"  # Deletes all 'a', 'b', and 'c'.

- A backslash (<tt>'\'</tt>) acts as an escape for a caret, a hyphen,
  or another backslash:

    s = 'abracadabra'
    s.delete('\^bc')           # => "araadara"   # Deletes all '^', 'b', and 'c'.
    s.delete('a\-c')           # => "brdbr"      # Deletes all 'a', '-', and 'c'.
    'foo\bar\baz'.delete('\\') # => "foobarbaz"  # Deletes all '\'.

These usages may be mixed:

  s = 'abracadabra'
  s.delete('a-cq-t') # => "d"         # Multiple ranges.
  s.delete('ac-d')   # => "brbr"      # Range mixed with plain characters.
  s.delete('^a-c')   # => "abacaaba"  # Range mixed with negation.

For multiple selectors, all forms may be used, including negations, ranges, and escapes.

  s = 'abracadabra'
  s.delete('^abc', '^def') == s.delete('^abcdef') # => true
  s.delete('a-e', 'c-g')   == s.delete('cde')     # => true
  s.delete('^abc', 'c-g')  == s.delete('defg')    # => true

Related: see {Converting to New String}[rdoc-ref:String@Converting+to+New+String].
