Create developers.html
removing extra linking policy blurb
semantic html - use of h3 instead of p+class
wordsmithing; adding links

- a few wordsmith-type changes
- added some more contextual links
- removed HREFs from the headings
strong and headings

- forgot to <strong> the link in the last paragraph for consistency
- changed h3 headings to h2
add link to `developers.html`
availble -> available
Rename developers.html to developer.html
changing /developers to /developer
removing the 'Draft' for API Standards
removing open source policy
reordering items and adding section titles
html changes

• changed heading hierarchy
• added section dividers
Merge pull request #88 from 18F/add-developer-hub

creating 18f.gsa.gov/developers