Update ch01.asciidoc

Clarifications and grammar suggestions
Update ch01.asciidoc

not "remove" but "replace"
Merge branch 'develop' of https://github.com/edeykholt/bitcoinbook into edeykholt-develop
Undoing the digital signature part, as signature that produces a signature sounds unnecessary
Reverting the mentioning of ATMs. While it's true, let's leave it to Andreas to update this chapter. We just finished half of 2014, and there is a lot that will change here in Bitcoin space. The previous sentence of using credit card is also already outdated
Reverting some more text back to the original text
Merge branch 'edeykholt-develop' into develop
Merge branch 'develop' of https://github.com/aantonop/bitcoinbook into develop