This PR fixes several issues so that it can compile without error and run the Whitespace example programs. I made these changes while adding it to wspace-lang/ws-corpus, a collection of currently 124 interpreters, compilers, programs, and other tools for Whitespace.

• Replace int with long long for stack/heap values and instruction arguments to give the largest range possible without using arbitrary-precision integers. This fixes programs that need larger integers, such as hanoi.ws.
• Replace int with size_t for indices to resolve signed/unsigned comparison warnings.
• Fix heap-related instructions (STORE, RETRIEVE, READC, and READN) and conditional branches (JUMPZERO and JUMPNEG).
• Initialize label map before execution so that labels after the program counter can be jumped to.
• Fix number argument parsing.
• Only print tokens and instructions when --verbose/-v flag is given.
• Interpret the file given by the filename, otherwise from stdin. Previously only hello_worldvanwiki.ws was interpreted.
• Indent consistently with 4 spaces. While reviewing, it may be useful to compare changes without this commit.

Fixes #9, fixes #5.