Individual postings may each have their own payee

If a posting has the metadata field "Payee" set to a string, that will
be used as the payee name for that posting.  This affects the register
report, the payees report, and the --by-payee option.

This is useful because sometimes I send, say, 4 checks at a time to my
bank.  So on my bank statement, this is all just one amount:

   2010-06-17 Sample
     Assets:Bank        $400.00
     Income:Check1     $-100.00
     Income:Check2     $-100.00
     Income:Check3     $-100.00
     Income:Check4     $-100.00

Though it's important that the Assets:Bank posting be a single posting
of $400 value, I'd like for income reports to show whom each check came
from.  Now I can say:

   2010-06-17 Sample
     Assets:Bank        $400.00
     Income:Check1     $-100.00  ; Payee: Person One
     Income:Check2     $-100.00  ; Payee: Person Two
     Income:Check3     $-100.00  ; Payee: Person Three
     Income:Check4     $-100.00  ; Payee: Person Four

When I report this, it appears as:

10-Jun-17 Sample             Assets:Bank             $400.00     $400.00
          Person One         Income:Check1          $-100.00     $300.00
          Person Two         Income:Check2          $-100.00     $200.00
          Person Three       Income:Check3          $-100.00     $100.00
          Person Four        Income:Check4          $-100.00           0

This shows that they are all in the same transaction (which is why the
date is not repeated), but they have different payees.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/report.h b/src/report.h
index eff375cc..a453d351 100644
--- a/src/report.h
+++ b/src/report.h
@@ -816,8 +816,9 @@ public:
          " %(justify(scrub(display_total), total_width, "
          "    4 + meta_width + date_width + payee_width + account_width"
          "      + amount_width + total_width + prepend_width, true, color))\n%/"
-         "%(justify(\" \", 2 + date_width + payee_width))"
-         "%$3 %$4 %$5\n");
+         "%(justify(\" \", date_width))"
+         " %(justify((has_tag(\"Payee\") ? payee : \" \"), payee_width))"
+         " %$3 %$4 %$5\n");
     });
 
   OPTION(report_t, related); // -r