Add EIP-6051: Private Key Encapsulation (ethereum#6051)

* added EIP draft for private key encapsulation

* minor updates to spec: intake function shall return the Ethereum address of the private key

* added test vector #1

* minor formatting

* minor edits

* added test vector ethereum#2 and ethereum#3, added signature verification data to #1

* changed signature to against byte values

* added test vector generator

* renamed file to assigned EIP number

* fixed file header

* updated default value for salt

* fixed offending links etc.

* fixed typo

Co-authored-by: xinbenlv <zzn@zzn.im>

* updated based on review comments

* replaced json formatting with none for better rendering

* fixed grammar

Co-authored-by: xinbenlv <zzn@zzn.im>

* fixed grammar

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* revision suggestions taken with gratitudes

Co-authored-by: xinbenlv <zzn@zzn.im>

* revision suggestions taken with gratitudes

Co-authored-by: xinbenlv <zzn@zzn.im>

* fixed grammar

Co-authored-by: xinbenlv <zzn@zzn.im>

* fixed grammar

Co-authored-by: xinbenlv <zzn@zzn.im>

* fixed grammar

Co-authored-by: xinbenlv <zzn@zzn.im>

* fixed grammar

Co-authored-by: xinbenlv <zzn@zzn.im>

* fixed grammar

Co-authored-by: xinbenlv <zzn@zzn.im>

* fixed grammar

Co-authored-by: xinbenlv <zzn@zzn.im>

* revision suggestions taken with gratitudes

Co-authored-by: xinbenlv <zzn@zzn.im>

* fixed grammar as suggested

Co-authored-by: xinbenlv <zzn@zzn.im>

* revision suggestions taken with gratitudes

Co-authored-by: xinbenlv <zzn@zzn.im>

* fixed grammar as suggested

Co-authored-by: xinbenlv <zzn@zzn.im>

* fixed grammar as suggested

Co-authored-by: xinbenlv <zzn@zzn.im>

* fixed grammar as suggested

* fixed based on grammarly.com suggestions

* Update EIPS/eip-6051.md

Co-authored-by: Pandapip1 <45835846+Pandapip1@users.noreply.github.com>

* Update EIPS/eip-6051.md

Co-authored-by: Pandapip1 <45835846+Pandapip1@users.noreply.github.com>

* Update EIPS/eip-6051.md

Co-authored-by: Pandapip1 <45835846+Pandapip1@users.noreply.github.com>

* replacing bold fonts with links as suggested

* fixed dead links

* fixed markdown linter errors

Co-authored-by: xinbenlv <zzn@zzn.im>
Co-authored-by: Pandapip1 <45835846+Pandapip1@users.noreply.github.com>