FEAT: added UNIXTIME codec for conversion of Rebol datetime! to Unix epoch number and back

Example:
```
encode 'unixtime 18-Sep-2019/9:06:45+2:00 ;== 1568790405
decode 'unixtime 1568790405 ;== 18-Sep-2019/9:06:45+2:00
```
string! and binary! is also supported as an input/output:
```
encode/as 'unixtime 18-Sep-2019/9:06:45+2:00 string! ;==  "5D81D785"
encode/as 'unixtime 18-Sep-2019/9:06:45+2:00 binary! ;== #{5D81D785}
decode 'unixtime  "5D81D785" ;== 18-Sep-2019/9:06:45+2:00
decode 'unixtime #{5D81D785} ;== 18-Sep-2019/9:06:45+2:00
```

Author: Oldes

src/mezz/boot-files.r

@@ -49,6 +49,7 @@ REBOL [
 	%mezz-crypt.r
 	%mezz-date.r ; Internet date support
 	%mezz-tail.r
+	%codec-unixtime.r
 	%codec-der.r
 	%codec-crt.r
 	%codec-gzip.r

src/mezz/codec-unixtime.r

@@ -0,0 +1,64 @@
+REBOL [
+	title:  "REBOL 3 codec for Unix time stamp"
+	name:   'codec-unixtime
+	author: "Oldes"
+	version: 0.1.0
+	date:    17-Sep-2019
+	history: [
+		0.1.0 17-Sep-2019 "Oldes" {Initial version}
+	]
+	urls: [
+		https://en.wikipedia.org/wiki/Unix_time
+		https://www.unixtimestamp.com
+	]
+]
+
+register-codec [
+	name:  'unixtime
+	title: "Unix time stamp converter"
+	suffixes: []
+
+	decode: function [
+		"Return date from unix time format"
+		epoch [number! string! binary!] "Date in unix time format (string is uspposed to be in base-16 format)"
+		/utc {Will not add time zone}
+	][
+		if string? epoch [ epoch: debase/base epoch 16 ]
+		if binary? epoch [ epoch: to integer! epoch ]
+		days: to integer! tmp: epoch / 86400
+		hours: to integer! time: (tmp - days) * 24
+		minutes: to integer! tmp: (time - hours) * 60
+		seconds: to integer! 0.5 + ((tmp - minutes) * 60)
+		time: to time! ((((hours * 60) + minutes) * 60) + seconds)
+		result: 1-Jan-1970 + days + time
+		unless utc [
+			result: result + now/zone
+			result/zone: now/zone
+		]
+		result
+	]
+
+	encode: function [
+		"Encode unix (epoch) time"
+		date [date!]
+		/as type [word! datatype!] {one of: [string! binary! integer!]}
+	][
+		time: any [date/time 0:0:0]
+		unix: ((date - 1-1-1970) * 86400)
+			+ (time/hour * 3600)
+			+ (time/minute * 60)
+			+  time/second
+			- to integer! (any [date/zone 0])
+		if as [
+			type: to word! type
+			binary/write bin: #{} [ui32 :unix]
+			switch type [
+				binary!  [ return bin ]
+				string!  [ return enbase/base bin 16]
+				integer! [ return unix ] ; just for consistency
+			]
+			cause-error 'script 'invalid-arg type
+		]
+		unix
+	]
+]

src/mezz/sys-codec.r

@@ -38,7 +38,7 @@ register-codec: function [
 decode: function [
  	{Decodes a series of bytes into the related datatype (e.g. image!).}
 	type [word!] {Media type (jpeg, png, etc.)}
-	data [binary! string!] {The data to decode}
+	data {The data to decode}
 ][
 	unless all [
 		cod: select system/codecs type
@@ -62,7 +62,8 @@ encode: function [
 	{Encodes a datatype (e.g. image!) into a series of bytes.}
 	type [word!] {Media type (jpeg, png, etc.)}
 	data {The data to encode}
-	/options opts [block!] {Special encoding options}
+	/as {Special encoding options}
+	 options {Value specific to type of codec}
 ][
 	unless all [
 		cod: select system/codecs type
@@ -74,7 +75,9 @@ encode: function [
 			do-codec cod/entry 'encode data
 		][
 			either function? try [:cod/encode][
-				cod/encode data
+				either as [
+					apply :cod/encode [data 'as options]
+				][	cod/encode data ]
 			][
 				cause-error 'internal 'not-done type
 			]

src/tests/units/codecs-test.r3

@@ -171,4 +171,32 @@ if find system/codecs 'tar [
 	system/codecs/tar/verbose: 1
 ]
 
+if find system/codecs 'unixtime [
+	===start-group=== "unixtime codec"
+		date: 18-Sep-2019/8:52:31+2:00
+		--test-- "encode 32bit unixtime"
+			--assert 1568789551  = encode 'unixtime date
+			--assert 1568789551  = system/codecs/unixtime/encode date
+			--assert  "5D81D42F" = encode/as 'unixtime date string!
+			--assert #{5D81D42F} = encode/as 'unixtime date binary!
+			--assert 1568789551  = encode/as 'unixtime date integer!
+			--assert error? try  [ encode/as 'unixtime date url! ]
+
+		--test-- "decode 32bit unixtime"
+			--assert date = decode 'unixtime 1568789551
+			--assert date = decode 'unixtime  "5D81D42F"
+			--assert date = decode 'unixtime #{5D81D42F}
+			--assert date = system/codecs/unixtime/decode 1568789551
+
+		date: 1-1-2056/1:2:3
+		--test-- "encode 64bit unixtime"
+			--assert 2713914123 = encode 'unixtime date
+			--assert "A1C30B0B" = encode/as 'unixtime date string!
+
+		--test-- "decode 64bit unixtime"
+			--assert date = decode 'unixtime 2713914123
+			--assert date = decode 'unixtime "A1C30B0B"
+	===end-group===
+]
+
 ~~~end-file~~~