backticks: adding backtick syntax experiment.

extra/backticks/authors.txt

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+John Benediktsson

extra/backticks/backticks-docs.factor

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+USING: help.markup help.syntax io.encodings.utf8 strings ;
+IN: backticks
+
+HELP: `
+{ $syntax "` command [args]`" }
+{ $description "Runs the specified command and captures the output as a " { $link utf8 } " encoded " { $link string } "." }
+{ $examples
+    { $unchecked-example
+        "` ls -l`"
+        "total 45\ndrwxrwxr-x+ 61 root  admin  2074 Apr  8 22:58 Applic..."
+    }
+} ;

extra/backticks/backticks.factor

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+! Copyright (C) 2015 John Benediktsson
+! See http://factorcode.org/license.txt for BSD license
+USING: fry io io.encodings.utf8 io.launcher multiline sequences
+unicode.categories ;
+IN: backticks
+
+SYNTAX: `
+    "`" parse-multiline-string [ blank? ] trim
+    '[ _ utf8 [ contents ] with-process-reader ]
+    append! ;

extra/backticks/summary.txt

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+Backtick process syntax