Prepare for v0.7.1

[adamgreig]

Includes:

• Deprecate msp::write Deprecate msp::write #297
• New syscall and bootstrap ASM Expose __syscall and add new bootstrap method #299
• More compiler fences Duplicate compiler fences around barrier instrs #311
• asm::delay timing fix Fix timing of asm-based delay implementation #312
• asm::delay clobber fix Fix __delay clobber #317
• LTO for ASM fix Use LTO instead of removing the panic handler manually. Closes #309 #318

Doesn't include anything to help with #304 which might be nice to fix but can come in 0.7.2 and might need some time to think about.

[rust-highfive]

r? @thalesfragoso

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[therealprof]

LGTM.

bors r+

[bors]

Build succeeded:

• ci-linux (1.38.0)
• ci-linux (stable)
• clippy
• rustfmt