Build fix for new compilers

Merge pull request #9 from denizzzka/build_fix

fix building on the new compilers

Compilation under 2.067

Workaround for bug:

• 14300

Null values fix

"null" string was interpreted as null value. Now you can pass null as empty string (or explicitly by null string).

Logging improvement

Pool now spams syntax errors in a logger.

Bug fixes

• Timestamp bug is fixed #4

Single row constraint

API update, new oneRowConstraint parameter:

    InputRange!(immutable Bson) execTransaction(string[] commands
        , string[] params = [], uint[] argnums = []
        , string[string] vars = null, bool[] oneRowConstraint = []) shared

If empty array then it is ignored. If it is non-empty it should be a length of the commands array. Each boolean value defines if i-th query from commands have to return only one row. If the query returns 0 or more than 1 rows - transaction is rollbacked and OneRowConstraintException is thrown.

PGNumeric native support

• PGNumeric was converted to string by default, it was leading to responds like this for arrays:

"[1,2,3]"

Now value of numeric[] would be converted to bson like:

[1,2,3]

Fixing linking problems

Avoiding linking problems when std.datetime.Interval invariant isn't generated by dmd.
See the invariant at: std.datetime.Interval:18404

Extracted from host application

• Asynchronous connection pool
• Transactions with multiple queries and responds
• Reversed libpq binary protocol
• All basic PostgreSQL types
• Testing suit