LICENSE CHANGE: MIT to MIT-0 (No Attribution)

[peterdemartini]

Switch to a more permissive, no attribution required, license so this code can be included upstream in Golang. No conflicts with any of the dependency licenses were found:

- github.com/yuin/goldmark @ v1.4.0 / v1.4.13 - MIT - https://github.com/yuin/goldmark/blob/master/LICENSE
- github.com/klauspost/cpuid/v2 @ v2.0.6 - MIT - https://github.com/klauspost/cpuid/blob/master/LICENSE
- github.com/mmcloughlin/avo @ v0.4.0 - MIT - https://github.com/mmcloughlin/avo/blob/master/LICENSE
- rsc.io/pdf - BSD-3 - https://github.com/rsc/pdf/blob/master/LICENSE
- golang.org/x/arch - BSD-3
- golang.org/x/crypto - BSD-3
- golang.org/x/mod - BSD-3
- golang.org/x/net - BSD-3
- golang.org/x/sync - BSD-3
- golang.org/x/sys - BSD-3
- golang.org/x/term - BSD-3
- golang.org/x/text - BSD-3
- golang.org/x/tools  - BSD-3
- golang.org/x/xerrors - BSD-3

Closes #84.

cc @achille-roussel @pelletier @kevinburkesegment @kalamay