[DOC] Harmonize #** methods

Author: BurdetteLamar

complex.c

@@ -1122,9 +1122,9 @@ complex_pow_for_special_angle(VALUE self, VALUE other)
 
 /*
  * call-seq:
- *   complex ** numeric -> new_complex
+ *   self ** exponent -> complex
  *
- * Returns +self+ raised to power +numeric+:
+ * Returns +self+ raised to the power +exponent+:
  *
  *   Complex.rect(0, 1) ** 2            # => (-1+0i)
  *   Complex.rect(-8) ** Rational(1, 3) # => (1.0000000000000002+1.7320508075688772i)

numeric.c

@@ -1390,9 +1390,9 @@ flo_divmod(VALUE x, VALUE y)
 
 /*
  *  call-seq:
- *    self ** other -> numeric
+ *    self ** exponent -> numeric
  *
- *  Raises +self+ to the power of +other+:
+ *  Returns +self+ raised to the power +exponent+:
  *
  *    f = 3.14
  *    f ** 2              # => 9.8596
@@ -4623,9 +4623,9 @@ rb_int_divmod(VALUE x, VALUE y)
 
 /*
  *  call-seq:
- *    self ** numeric -> numeric_result
+ *    self ** exponent -> numeric
  *
- *  Raises +self+ to the power of +numeric+:
+ * Returns +self+ raised to the power +exponent+:
  *
  *    2 ** 3              # => 8
  *    2 ** -3             # => (1/8)
@@ -4748,8 +4748,7 @@ fix_pow(VALUE x, VALUE y)
  *  call-seq:
  *    self ** exponent -> numeric
  *
- *  Returns the value of base +self+ raised to the power +exponent+;
- *  see {Exponentiation}[https://en.wikipedia.org/wiki/Exponentiation]:
+ *  Returns +self+ raised to the power +exponent+:
  *
  *    # Result for non-negative Integer exponent is Integer.
  *    2 ** 0   # => 1

rational.c

@@ -984,9 +984,9 @@ nurat_fdiv(VALUE self, VALUE other)
 
 /*
  * call-seq:
- *    rat ** numeric  ->  numeric
+ *    self ** exponent -> numeric
  *
- * Performs exponentiation.
+ * Returns +self+ raised to the power +exponent+:
  *
  *    Rational(2)    ** Rational(3)     #=> (8/1)
  *    Rational(10)   ** -2              #=> (1/100)