Input/Output native support for BigInteger and BigDecimal

[ghik]

Add writeBigInteger and writeBigDecimal methods to Output trait.
Add readBigInteger and readBigDecimal methods to Input trait.

[ghik]

This along with configurable MathContext in #66 should solve #65

[plokhotnyuk]

Also, limits for the scale should be configurable (with some defaults like ±300 provided) to resolve #65