Embed json schema in binary

[adrienjoly]

See SchemaLocation.

So that we cam add a new comment format and test it from another directory before the schema was uploaded to https://fbiville.github.io/headache/schema.json.

=> The binary should not have to download that schema at every run.

Environment

• headache version:
• Git repository URL (if possible):
• contents of .headache-run:

.headache-run contents to insert here

• latest revision of .headache-run (git --no-pager log --format='%H' -1 -- .headache-run): edit this
• contents of JSON configuration (default name: headache.json):

JSON configuration contents to insert here

• contents of the license header template:

header template contents to insert here

Protips

the following only applies to duplicated or malformed header issues

headache can be quite sensitive to small differences between the header template and the actual headers in source files, especially at the first run!

Here a few things to check before reporting an issue:

• the configuration JSON file and header template have not been changed since .headache-run last revision
• there are no differences between the affected source file's header and the header in configured template file

Describe the bug
A clear and concise description of what the bug is.
If it concerns duplicated/malformed headers, please include the full contents of at least one affected source file:

source file contents to insert here

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'

Expected behavior
A clear and concise description of what you expected to happen.

Additional context
Add any other context about the problem here.