BufferTime is now a private field initialized in the constructor, it
can't be changed during the lifetime of NyaaPatterns.
Made Countdown accept a possible T-Minus Seconds value.
Also pretified some code and made the irc field readonly.
Updated the help of .cd
Made several fields readonly
* Calculation.cs: Small changes to AddNumToExpr.

* IrcCalc.cs:
* MiscUtils.cs: Made some fields readonly.