array: s/last/len. Closes #3
Replace "compulsory"

I don't know about other non-native speakers, but I sometimes have
trouble remembering what "compulsory" means. "mandatory" is better, but
it can also be written in simpler words.
Merge pull request #12 from robinst/patch-1

Replace "compulsory"
Fix edit and contribute button. Closes #4
Merge pull request #13 from jcdyer/master

Minor additions and edits (through section 17)
Fix typo in #13
Update input.md

Fixes typo on literals page
Merge pull request #16 from rossmurray/patch-1

Update input.md
bounds: fix grammar. Closes #14
box: Briefly explain references. Closes #11
added a page for unsafe operations
Minor fix 

get allocated -> gets allocated
match.rs: Formatting: Each branch on separate line

Putting each branch on a new line and terminating each branch with a
comma is consistent with the other examples in this source file, and
less confusing. The comma isn't strictly necessary when the previous
branch ends with a "}" but it's more consistent.

I experimented with a more comprehensive check for code formatting
throughout this tutorial by running `rustc --pretty` in the makefile,
but `rustc --pretty` is a bit too idiosyncratic: It forces a newline
before each comment, it sometimes puts spaces before commas, and it adds
unnecessary quoting like "ain\'t".
Fix grammar.
Link to issue #1 for convenience.
Merge pull request #21 from joeyespo/master

Link to issue #1 for convenience
Merge pull request #20 from numerodix/master

Fix grammar.
Merge pull request #19 from drothlis/match-formatting

match.rs: Formatting: Each branch on separate line
Merge pull request #18 from timClicks/patch-1

Minor fix
Addressed diff comments by japaric