Add option to output numeric data types as string. (yugabyte#255)

Add option to output numeric data types as string.

Data types like `numeric`, `real`, `double precision` supports `Infinity`,
`-Infinity` and `NaN` values. Currently these values output as `null` because
JSON specification does not recognize them as valid numeric values. This will
create problems for the users of wal2json who need these values to maintain
data integerity.

Makefile

@@ -4,7 +4,7 @@ REGRESS = cmdline insert1 update1 update2 update3 update4 delete1 delete2 \
 		  delete3 delete4 savepoint specialvalue toast bytea message typmod \
 		  filtertable selecttable include_timestamp include_lsn include_xids \
 		  include_domain_data_type truncate type_oid actions position default \
-		  pk rename_column
+		  pk rename_column numeric_data_types_as_string
 
 PG_CONFIG = pg_config
 PGXS := $(shell $(PG_CONFIG) --pgxs)

README.md

@@ -109,6 +109,7 @@ Parameters
 * `include-not-null`: add _not null_ information as _columnoptionals_. Default is _false_.
 * `include-default`: add default expression. Default is _false_.
 * `include-pk`: add _primary key_ information as _pk_. Column name and data type is included. Default is _false_.
+* `numeric-data-types-as-string`: use string for numeric data types. JSON specification does not recognize `Infinity` and `NaN` as valid numeric values. There might be [potential interoperability problems](https://datatracker.ietf.org/doc/html/rfc7159#section-6) for double precision numbers. Default is _false_.
 * `pretty-print`: add spaces and indentation to JSON structures. Default is _false_.
 * `write-in-chunks`: write after every change instead of every changeset. Only used when `format-version` is `1`. Default is _false_.
 * `include-lsn`: add _nextlsn_ to each changeset. Default is _false_.