Templates for defining data types/etc

[solemnwarning]

Something akin to 010 Editor's Binary Templates... maybe even use the same format if it isn't unreachable.

Also a visual editor for the templates might be interesting... along with extra features like setting comments from the template.

[solemnwarning]

WIP support for 010-style Binary Templates is now working on the binary-template branch.

Still missing lots of functionality, but any relatively simple template will probably work.

Things that still need doing:

• Implement distinct number types (int/double, signed/unsigned, clamping values to type limits)
• Make string and char[] interchangable
• Reference types as function parameters
• Increment (++) and decrement (--) operators
• do-thing-and-assign shorthand operators (+=, -=, *=, etc)
• Write a manual...
• Integration tests for preprocessor/parser/executor
• Clean up error reporting in executor
• Don't cross struct boundaries when resolving variables (and types?)
• Add to CI coverage report
• Scope variables/types within blocks
• Don't allow function declarations inside other blocks
• Tidy up UI
• Allow operating on a range/selection rather than the whole file
• Run template in a transaction
• Yield when reading huge amounts of file data
• Ternary operator
• Parse x-1 as (x) (-) (1) rather than (x) (-1)
• Hex and octal numbers
• Populate array from a loop syntax
• Declare anonymous enum variables
• Fix random failures in parser...
• Make array_extend() on empty file arrays work (don't depend on data_range)
• Add template output window
• Remember templates selected by "Browse" button

Things I'm probably not going to support in the first version:

• Bitfields
• Unions
• Variable attributes (comments, disasm, etc)
• Add checker for program structure, names/types/etc before passing to executor
• Lexical variable scoping across function/struct boundaries

Things I'm not going to support:

• DLL functions

Expect all of the above lists to grow.