Execute all line continuations in immediate mode

Hello again,

I was surprised when I tried `a=3:b=7` in BLBasic's immediate mode and it ignored the `b=7` part, so I added some code to make it not do that.

Some combinations won't do what you might expect, like `run:print "hi"` (prints "hi" before running the program.)  This is related to the logic for how to start the program, which (basically) sets a variable to say "start program execution from this point", which isn't checked until the line is finished; in a similar vein, `goto 10` from immediate mode does nothing (before or after this change.)

Not entirely sure what your vision for BLBasic is, so I'm not sure whether it's more appropriate making `run` and `goto` from immediate mode do what an 8-bit BASIC user in the 80's would expect, or more appropriate to just leave it how it is, as a sort of BLBasic-ism.

In the process of making this change, I also looked into the TODO item about calling `deleteLines` in immediate mode, and it seems to work fine (and plug a memory leak), so I made that change too.

Cheers,
-Chris