141. implement btoa()

btoa() accepts a binary string and returns a Base64-encoded ASCII string from it. Characters in a binary string are the ASCII character for each byte of the binary data.

Please read Base64 wiki and implement your own btoa().

myBtoa('BFE')
// 'QkZF'

myBtoa('BFE.dev')
// 'QkZFLmRldg=='

note

1. Please don't use window.btoa() in your code.
2. The binary string passed to your function are all valid ASCII characters, there will be another problem on the general Base64 encoding/decoding.