BigInt literals now accept binary and octal formats

[bamarsha]

microsoft/qsharp-compiler#673 added support for binary and octal BigInt literals to the compiler. The documentation on BigInt Literals in the Q# specification should be updated.

[bamarsha]

@ziqi-ma in case you also wanted to update the documentation. :) If not, I or someone else can get to it soon.

[ziqi-ma]

Sent in PR:)