TODO

* Modernize file location
* Use TypedData
* Preserve scale of zeros
* Implement "decimal/compat/bigdecimal", a bigdecimal-compatible layer
* Be a good friend with other Numeric classes (using Kernel.autoload?)
  - OtherNumerics#to_decimal, Decimal#to_*
* Define `marshal_dump' and `marshal_load'

* Implement Decimal::Math.pi / Decimal::Math.e with a precise option
* Decimal#format_s based on format of Excel
* Embedded decimal32/64 (that size equals to pointer's)
* Static value for well-used value like 0, 1 or 10 ?

done:
- Implement decimal ** otherdecimal and decimal ** -integer
- Implement Math functions
- Implement webpages
- Support RubyGems
- Support Ruby 1.9
- Implement NaN/+-Infinity as a singleton object
- Write tests
- Write RDocs
- Implement decimal ** fixnum 
- Create .document
- GMP support with "--with-gmp" and inumgmp.h (via Ruby 2.1)