radix conversion

• default alphabet is '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_' for input and output
• you can change it by passing different alphabets to the BaseConv exported function
• no IEEE-754 limitation

usage:

const conv = require('base-conv').default;
conv(42, 10, 16) // '2a'
conv('42', 10, 16) // '2a'
conv('42'.repeat(100), 10, 16) // '8de2991df40ff783057818d0012f3bc1c...'