Implement a data segment

[ralfgerlich]

Defining data contents is quite tedious now: One has to write code that places the data somewhere in memory - currently only the stack is available for that - and the data cannot be referred to by labels. There is some support for generating this code using the "Code Gen Save String" example, which queries for a string and outputs the code to be used for storing it in memory, but again, this is tedious to use.

The MARS Emulator - which seems to have been a bit of an inspiration for WeMIPS - provides a separate .data segment and some directives - including an .asciiz directive - to define data contents, and a .text directive to introduce actual assembly code. We could implement something similar to that.

A good start would be to implement the follwing

• .data directive to introduce data declarations
• .text directive to introduce code definitions (without any directives used, this would be the default at the start)
• .word directive to fill the data segment with word-sized entries (signed or unsigned)
• labels in data space referring to data locations