check types used to parse CIL operands

[mike-hunhoff]

ensure signed/unsigned values used as defined by the spec.

see https://en.wikipedia.org/wiki/List_of_CIL_instructions.

see #18 (comment).

[mike-hunhoff]

checked:

• inline branch
• inline field
• inline_i
• inline_i8
• inline_method
• inline_none
• inline_phi
• inline_r
• inline_sig
• inline_string
• inline_switch
• inline_tok
• inline_type
• inline_var
• short_inline_br_target
• short_inline_i
• short_inline_r
• short_inline_var
• read_opcode
• parse_header
• parse_exception_handlers
• parse_fat_exception_handlers
• parse_tiny_exception_handlers

to update:

• ldc.i4
• ldc.i8
• ldc.i4.s

[mike-hunhoff]

double-checked and fixed reader types - I could not find explicit definitions for the types used to parse exception handler data. assuming unsigned works for these - we can reopen in the future if we encounter any issues.