pgsql: Add \pset options for boolean value display

Add \pset options for boolean value display

New \pset variables display_true and display_false allow the user to
change how true and false values are displayed.

Author: David G. Johnston <David(dot)G(dot)Johnston(at)gmail(dot)com>
Reviewed-by: Álvaro Herrera <alvherre(at)kurilemu(dot)de>
Discussion: https://postgr.es/m/CAKFQuwYts3vnfQ5AoKhEaKMTNMfJ443MW2kFswKwzn7fiofkrw@mail.gmail.com
Discussion: https://postgr.es/m/56308F56.8060908@joh.to

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/645cb44c5490f70da4dca57b8ecca6562fb883a7

Modified Files
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doc/src/sgml/ref/psql-ref.sgml | 20 +++++++++++++++++++
src/bin/psql/command.c | 41 +++++++++++++++++++++++++++++++++++++-
src/bin/psql/help.c | 10 +++++++---
src/bin/psql/tab-complete.in.c | 3 ++-
src/fe_utils/print.c | 4 ++++
src/include/fe_utils/print.h | 2 ++
src/test/regress/expected/psql.out | 32 +++++++++++++++++++++++++++++
src/test/regress/sql/psql.sql | 16 +++++++++++++++
8 files changed, 123 insertions(+), 5 deletions(-)