Update bitcoin-for-developers.html

grammar fix
use "digital currency" to keep consistence with the title
fix Mac OS X download link
Merge pull request #101 from mode80/master

small grammar fix
mobile responsive design and many design fixes
adapt CSS to be either responsive, or specific to mobiles
add mobile menu icon to show the hidden menu on touch
add optimized language bar menu for mobiles
remove 1200px width workaround for the wallet page, description now fit on 1
remove links on wallet icons for :hover compatibility with mobile devices
move right buttons into the page (fixes #67)
fix contributors plugin to produce W3C valid HTML
drop useless classes like .list
clean and organize CSS
add icon for ios touch devices (fixes #111)
Merge pull request #110 from bitcoin/mobile

mobile responsive design and many design fixes
fix many small typo and update README guidelines
fix wrong encoding for some space characters in the french version
fix lowercase/uppercase "bitcoin" depending if we speak of the unit or the technology
update some french translation to fit recent english changes
add guidance about previewing fixed height/width texts and ask for UTF-8 encoded texts in the README
fix typos in the french version
resize some client icons so they appear at the same size
fix transparency of Bitcoin Wallet client icon
Merge pull request #114 from schildbach/harmonize-client-icons

resize some client icons so they appear at the same size
mention OS in the README (fixes #109)
Add hovers to the small platform icons.
Merge pull request #115 from schildbach/platform-icons-hover

Add hovers to the small platform icons.
fix mobile detection for higher DPI devices
remove instawallet (service compromised and suspended) (fixes #117)
add translations tracking instructions in the README
small french typo
Small improvements in the text about anonymity
Use a shorter and straightforward title and a clearer explanation
Prepare main CSS to custom CSS per language
Adapt top menu to right-to-left dir
Turn all font-size to percentages