Externalize some internal variables

[wcampbell0x2a]

Allow some replacement of text in Input.

Mapping

It's very common to need to copy+past certain memory locations when settings breakpoints.

7f741861f000-7f7418645000 r--p 00000000 fe:01 32245210                   /usr/lib/x86_64-linux-gnu/libc.so.6
7f7418645000-7f741879a000 r-xp 00026000 fe:01 32245210                   /usr/lib/x86_64-linux-gnu/libc.so.6
7f741879a000-7f74187ed000 r--p 0017b000 fe:01 32245210                   /usr/lib/x86_64-linux-gnu/libc.so.6
7f74187ed000-7f74187f1000 r--p 001ce000 fe:01 32245210                   /usr/lib/x86_64-linux-gnu/libc.so.6
7f74187f1000-7f74187f3000 rw-p 001d2000 fe:01 32245210                   /usr/lib/x86_64-linux-gnu/libc.so.6

Maybe, b *($VAR_MAPPING_START_/usr/lib/x86_64-linux-gnu/libc.so.6:0) to mean the first? => b *(0x7f741861f000), VAR_MAPPING_END => 0x7f7418645000

[wcampbell0x2a]

This is mostly done, but keeping around as a discussion to allow more requests for internal variables.