Format listed issues plainly when STDIN is not a TTY

When calling pit from other programs or as part of a pipe, the display
style typically used to format listed issues contains a lot of unwanted
output (ANSI escape code, headings, etc.). Now when STDIN is not a TTY,
a plain and consistently formatted version of the issues is listed
without any additional formatting, one issue per line of output.

src/pitpkg/cliconstants.nim

@@ -1,4 +1,4 @@
-const PIT_VERSION* = "4.24.1"
+const PIT_VERSION* = "4.25.0"
 
 const USAGE* = """Usage:
   pit ( new | add) <summary> [<state>] [options]