Added usage statements for C<chr>, C<expmod>, and C<is-prime>

lib/Type/Int.pod

@@ -23,24 +23,46 @@ separators, but don't carry any meaning:
 
 =head2 routine chr
 
+Defined as:
+
     multi sub    chr(Int:D ) returns Str:D
     multi method chr(Int:D:) returns Str:D
 
+Usage:
+
+    chr INTEGER
+    INTEGER.chr
+
 Returns a one-character string, by interpreting the integer as a Unicode
 codepoint number and converting it the corresponding character.
 
 =head2 routine expmod
 
+Defined as:
+
     multi sub    expmod (Int:D: Int $y, Int $mod) returns Int:D
     multi method expmod (Int:D: Int $y, Int $mod) returns Int:D
 
+Usage:
+
+    expmod(INTEGER, POWER, MODULUS)
+    INTEGER.expmod(POWER, MODULUS)
+
 Returns the given C<Int> raised to the C<$y> power within modulus C<$mod>.
 
 =head2 routine is-prime
 
+Defined as:
+
     multi sub    is-prime (Int:D $number, Int $tries = 100) returns Bool:D
     multi method is-prime (Int:D: Int $tries = 100) returns Bool:D
 
+Usage:
+
+    is-prime INTEGER
+    INTEGER.is-prime
+    INTEGER.is-prime
+
 Returns C<True> if this C<Int> is known to be a prime, or is likely to be a
 prime based on a probabilistic Miller-Rabin test. C<$tries> is the maximal
 number of iterations the test is allowed to do.