syntax: highlight all known directives

Acording to <http://ledger-cli.org/3.0/doc/ledger3.html>

Signed-off-by: Roland Hieber <rohieb@rohieb.name>

Author: rohieb

syntax/ledger.vim

@@ -48,6 +48,10 @@ syn match ledgerPreDeclarationType /^\(account\|payee\|commodity\|tag\)/ contain
 syn match ledgerPreDeclarationName /^\S\+\s\+\zs.*/ contained
 syn match ledgerPreDeclarationDirective /^\s\+\zs\S\+/ contained
 
+syn match ledgerDirective
+  \ /^\%(alias\|assert\|bucket\|capture\|check\|define\|expr\|fixed\|include\|year\)\s/
+syn match ledgerOneCharDirective /^\%(P\|A\|Y\|N\|D\|C\)\s/
+
 syn match ledgerComment /^;.*$/
 " comments at eol must be preceded by at least 2 spaces / 1 tab
 syn region ledgerMetadata start=/\%(  \|\t\|^\s\+\);/ skip=/^\s\+;/ end=/^/
@@ -84,6 +88,8 @@ highlight default link ledgerAmount Number
 highlight default link ledgerPreDeclarationType Type
 highlight default link ledgerPreDeclarationName Identifier
 highlight default link ledgerPreDeclarationDirective Type
+highlight default link ledgerDirective Type
+highlight default link ledgerOneCharDirective Type
 
 " syncinc is easy: search for the first transaction.
 syn sync clear