Sets the bit at zero-based bit +offset+ to 1; returns +self+:

  s = "\x00"
  s.bit_set(1) # => "\x02"
  s            # => "\x02"

With +length+, sets the +length+ consecutive bits beginning at +offset+;
with a Range, sets the bits covered by +range+:

  s = "\x00\x00"
  s.bit_set(4, 8)  # => "\xF0\x0F"
  s = "\x00\x00"
  s.bit_set(4..11) # => "\xF0\x0F"

The entire region must lie within +self+; a region that extends beyond the
end raises +IndexError+ rather than being clamped. Writing zero bits is a
no-op, but even an empty region raises +IndexError+ when it begins beyond
the end of +self+.

By default, bits within each byte are numbered from least-significant to
most-significant. If +lsb_first+ is +false+, byte order is unchanged but bits
within each byte are numbered from most-significant to least-significant:

  s = "\x00"
  s.bit_set(1, lsb_first: false) # => "\x40"
  s = "\x00\x00"
  s.bit_set(4, 8, lsb_first: false) # => "\x0F\xF0"

Raises +IndexError+ if +offset+ is out of range, or if any part of the
region lies outside +self+.
Raises +ArgumentError+ if +length+ is negative.
Raises +ArgumentError+ if a bit position is too large to be represented.
Raises +ArgumentError+ if +lsb_first+ is neither +true+ nor +false+.
Raises +FrozenError+ if +self+ is frozen, even when writing zero bits.