abandoned yaml, perl and c key exporters, added json exporter using libjansson, enable with --with-json

man/options.pod

@@ -62,12 +62,9 @@
  -K --import               Import a key. pcp determines automatically
     --import-key           the key type and encodingg. Use -I to import
                            from a file.
- -y --export-yaml          Export all keys stored in your vault
-                           as YAML formatted text. Use -O to put
-                           the export into a file.
  -F --format               Export the key in a particular format.
-                           Currently supported: pcp, pbp, yaml,
-                           perl and C.
+                           Currently supported: pcp and pbp.
+ -j --json                 enable JSON ex- and import of keys.
  
  Encryption Options:
  -e --encrypt              Asym-Encrypt a message. Read from stdin or