Finished an incomplete section + typo fix

Explaination - > explanation
Wrote brief blurbs on the capabilities of the debugger stepping buttons, all of which were previously incomplete/missing.

Fixed a typo.

There is a typo in the error message.

bumped version to v0.10.3

bump the version to v0.10.2

bumpVersion v0.10.0 -> v0.10.1

Merge pull request ethereum#2736 from ethereum/bumpVersion

bump the version to v0.10.0

Merge pull request ethereum#2578 from ethereum/bumpVersion0.9.4

bump 0.9.4

release 0.9.3

updated package-lock

package-lock updated