Add Gitlab CI

Closes #1

See merge request !1

Fix dead green card links

Rebuild riscv-card.pdf to resolve merge conflict.

Add Travis-CI build badge, rewritten intro and contents

Fix temporary register mapping

Opcode fixes and improved consistency for funct7 field

F3 -> funct3 in table headers

Same as what previous commit did for F3 -> funct3.

Same as what previous commit did for F3 -> funct3.

addi, xori, ori and addi had the exact same encoding. Use the right F3
field from https://riscv.org/specifications/ (page 146).

The field is called funct3 elswhere in the same document and in the
official specification. Use the same name everywhere for consistency.

Fixed opcode values for R-Type

* Create .travis.yml

Add continous integrations over travis-ci.