Add support for filtering based on property exclusion.

For example, allow commands like:

  # exclude issues from context "abc"
  pit list -C abc

  # exclude issues delegated to John Doe
  pit list -P "delgated-to:John Doe"

src/pitpkg/cliconstants.nim

@@ -1,4 +1,4 @@
-const PIT_VERSION* = "4.18.2"
+const PIT_VERSION* = "4.19.0"
 
 const USAGE* = """Usage:
   pit ( new | add) <summary> [<state>] [options]
@@ -25,7 +25,18 @@ Options:
                             a filter to the issues listed, only allowing those
                             which have all of the given properties.
 
-  -c, --context <ctxName>   Shorthand for '-p context:<ctxName>'
+  -P, --excl-properties <props>
+                            When used with the list command, exclude issues
+                            that contain properties with the given value. This
+                            parameter is formatted the same as the --properties
+                            parameter: "key:val;key:val"
+
+  -c, --context <ctx>       Shorthand for '-p context:<ctx>'
+
+  -C, --excl-context <ctx>  Don't show issues from the given context(s).
+                            Multiple contexts can be excluded using a ',' to
+                            separate names. For example: -C ctx1,ctx2
+                            Shorthand for '-P context:<ctx>'
 
   -g, --tags <tags>         Specify tags for an issue.
 
@@ -48,7 +59,7 @@ Options:
 
   -y, --yes                 Automatically answer "yes" to any prompts.
 
-  -C, --config <cfgFile>    Location of the config file (defaults to $HOME/.pitrc)
+  --config <cfgFile>        Location of the config file (defaults to $HOME/.pitrc)
 
   -E, --echo-args           Echo arguments (for debug purposes).
 
@@ -155,4 +166,4 @@ Issue Properties:
 
       If present, expected to be a comma-delimited list of text tags. The -g
       option is a short-hand for '-p tags:<tags-value>'.
-"""
+"""