Removed const esc sequence

[andres-lowrie]

Addresses: https://github.com/DrakeW/corgi/issues/34

Offloads all terminal coloring to fatih/color

---

How I did testing:

# From `develop`
go build
./corgi new -t exporttest
# Make a command

./corgi export exporttest
./corgi export exporttest -t shell
mv exporttest{,_beforechanges}.json
mv exporttest{,_beforechanges}

git checkout branch
go build
./corgi export exportest
./corgi export exportest -t shell

# There should be no differences
diff exporttest exporttest_beforechanges
diff exporttest.json exporttest_beforechanges.json

[andres-lowrie]

Forgot this bit:

I used ripgrep to see usage of the const escape sequence:

rg "SHELL_GREEN|SHELL_RED|SHELL_YELLOW|SHELL_NO_COLOR"

[junyu-w]

@andres-lowrie thanks for the PR, I've reviewed and overall this looks solid!

[andres-lowrie]

Finally got some down time (yay holidays!!)

I believe I addressed the points you mentioned. I also rebased the branch for a cleaner commit message.

Lmk if this needs anything else!

Happy Holiday!