PE: TLS parser generics and bitness-related rework

[kkent030315]

Reference: #425 (comment)

TL;DR:

• Deprecate TlsData::parse, TlsData::parse_with_opts that uses unintuitive generics.
  • Instead, we should ideally have is_64.
• Make independent ImageTlsDirectory(64) and ImageTlsDirectory32, and impl <From<ImageTlsDirectory32>> for ImageTlsDirectory(64) to merge.