Bug 939367 - Part 2: Move requirements.txt into tools/docs

Trivial change. No review.

DONTBUILD (NPOTB)

--HG--
rename : build/docs/requirements.txt => tools/docs/requirements.txt
Bug 948839 Mark special flag of drag over event true if it's consumed on content r=smaug
Bug 938406 - DataStore - proper event sent when the first revision is created, r=ehsan
Bug 949038 - Fix windows browser build error in jsweakmap.h with generational GC r=terrence
Bug 948423 - Use relookupOrAdd() to insert into has type representation hash map following possible mutation by GC r=sfink
Bug 948914 - Remove redundant default style for <pre> element from quirk.css. r=dbaron
Bug 945634. The fixed-pos anchor point should be in the layer's coordinate system, whose 0,0 is the top-left of the fixed-pos frame. r=mattwoodrow
Bug 948777 - Build netwerk/sctp/src in unified mode; r=jesup
Bug 949360 - Check for Image AllocateBuffer() failures. r=nical
Bug 939614: IonMonkey: Add recompile check, r=jandem
Bug 939614: IonMonkey: Split IonOptions in IonOptions and IonOptimizations, r=jandem
Bug 939614: IonMonkey: Rename IonOption to JitOption, r=jandem
Bug 939614: IonMonkey: Use logic in UsesBeforeCompile to get actual needed usecount, r=jandem
Bug 939614: IonMonkey: Enable reschedule same optimizationLevel if osrPc is different, r=jandem
Bug 939614: IonMonkey: Properly spew recompiling instead of analyzing, r=jandem
Bug 948992 - Copy the deviceSerial to ADB's device manager. r=jgriffin
Bug 778236 - Treat gyp files as if their content was defined in moz.build files. r=gps
Bug 778236 - Remove EXTERNAL_MAKE_DIRS and PARALLEL_EXTERNAL_MAKE_DIRS. r=gps
Merge mozilla-central to mozilla-inbound
Bug 949401 - Marionette python client is missing resources from latest marionette_client 0.7.0, r=mdas