Add missing documentation to some coder classes

... and mention that they require extensions on first use.

Author: larskanis

ext/pg_binary_decoder.c

@@ -233,6 +233,8 @@ j2date(int jd, int *year, int *month, int *day)
  *
  * This is a decoder class for conversion of PostgreSQL binary date
  * to Ruby Date objects.
+ *
+ * As soon as this class is used, it requires the ruby standard library 'date'.
  */
 static VALUE
 pg_bin_dec_date(t_pg_coder *conv, const char *val, int len, int tuple, int field, int enc_idx)

ext/pg_text_decoder.c

@@ -163,6 +163,8 @@ pg_text_dec_integer(t_pg_coder *conv, const char *val, int len, int tuple, int f
  * This is a decoder class for conversion of PostgreSQL numeric types
  * to Ruby BigDecimal objects.
  *
+ * As soon as this class is used, it requires the 'bigdecimal' gem.
+ *
  */
 static VALUE
 pg_text_dec_numeric(t_pg_coder *conv, const char *val, int len, int tuple, int field, int enc_idx)
@@ -811,6 +813,7 @@ static VALUE pg_text_dec_timestamp(t_pg_coder *conv, const char *val, int len, i
  * This is a decoder class for conversion of PostgreSQL inet type
  * to Ruby IPAddr values.
  *
+ * As soon as this class is used, it requires the ruby standard library 'ipaddr'.
  */
 static VALUE
 pg_text_dec_inet(t_pg_coder *conv, const char *val, int len, int tuple, int field, int enc_idx)

ext/pg_text_encoder.c

@@ -345,6 +345,8 @@ pg_text_enc_float(t_pg_coder *conv, VALUE value, char *out, VALUE *intermediate,
  *
  * It converts Integer, Float and BigDecimal objects.
  * All other objects are expected to respond to +to_s+.
+ *
+ * As soon as this class is used, it requires the 'bigdecimal' gem.
  */
 static int
 pg_text_enc_numeric(t_pg_coder *this, VALUE value, char *out, VALUE *intermediate, int enc_idx)

lib/pg/text_decoder/date.rb

@@ -5,6 +5,9 @@
 
 module PG
 	module TextDecoder
+		# This is a decoder class for conversion of PostgreSQL date type to Ruby Date values.
+		#
+		# As soon as this class is used, it requires the ruby standard library 'date'.
 		class Date < SimpleDecoder
 			def decode(string, tuple=nil, field=nil)
 				if string =~ /\A(\d{4})-(\d\d)-(\d\d)\z/

lib/pg/text_decoder/json.rb

@@ -5,6 +5,9 @@
 
 module PG
 	module TextDecoder
+		# This is a decoder class for conversion of PostgreSQL JSON/JSONB type to Ruby Hash, Array, String, Numeric, nil values.
+		#
+		# As soon as this class is used, it requires the ruby standard library 'json'.
 		class JSON < SimpleDecoder
 			def decode(string, tuple=nil, field=nil)
 				::JSON.parse(string, quirks_mode: true)

lib/pg/text_encoder/date.rb

@@ -3,6 +3,7 @@
 
 module PG
 	module TextEncoder
+		# This is a encoder class for conversion of Ruby Date values to PostgreSQL date type.
 		class Date < SimpleEncoder
 			def encode(value)
 				value.respond_to?(:strftime) ? value.strftime("%Y-%m-%d") : value

lib/pg/text_encoder/inet.rb

@@ -5,6 +5,9 @@
 
 module PG
 	module TextEncoder
+		# This is a encoder class for conversion of Ruby IPAddr values to PostgreSQL inet type.
+		#
+		# As soon as this class is used, it requires the ruby standard library 'ipaddr'.
 		class Inet < SimpleEncoder
 			def encode(value)
 				case value

lib/pg/text_encoder/json.rb

@@ -5,6 +5,9 @@
 
 module PG
 	module TextEncoder
+		# This is a encoder class for conversion of Ruby Hash, Array, String, Numeric, nil values to PostgreSQL JSON/JSONB type.
+		#
+		# As soon as this class is used, it requires the ruby standard library 'json'.
 		class JSON < SimpleEncoder
 			def encode(value)
 				::JSON.generate(value, quirks_mode: true)