Some fixes
Implemented missing tools functions

- string_to_bytes
- hex_to_bytes
- base64_to_bytes
Minor fixes
BigNumber: basic operations
BigNumber: refactoring, O(1) stack allocator for asm.js module, tests, fixes
BigNumber: Modulus operations

 * modulus reduction by division,
 * buggy Montgomery reduction,
 * pseudo-Mersenne primes generator, and
 * precomputed primes table up to 2^(32*128) (not all primes are found for now)
BigNumber: fix `splice`, fix Montgomery reduction, 4 more primes found
BigNumber: fixes, asm.js Montgomery reduction

TODO HAC 14.32
BigNumber: asm.js implementation of HAC 14.32 reduction

Also drop (pseudo-)Mersenne primes table and all the related stuff for now,
maybe later it'll be back.
BigNumber: modular exponentiation
BigNumber: fix HAC 14.32 reduction, fix modular exponentiation
RSA: initial commit
RSA: add ASN1 parser as submodule
RSA: parse keys
RSA: encrypt/decrypt and tests
RSA-OEAP, no tests at now
BigNumber: primality test, begin work on RSA key generation
RSA: generateKey
RSA-PKCS1: some fixes, OAEP test
RSA-PSS: sign/verify, test