misc: designate _build/out as the build output directory

This is so that we could later add other build-related files under the
_build directory and keep track in git.

Change-Id: Ida3a3062a13e8050d745d71a428b7fb687ea4b81

.gitignore

@@ -1 +1 @@
-_build/
+_build/out

.tx/config

@@ -3,36 +3,36 @@ host = https://www.transifex.com
 
 [o:savoirfairelinux:p:jami:r:docs-user]
 file_filter = locales/<lang>/LC_MESSAGES/user.po
-source_file = _build/gettext/user.pot
+source_file = _build/out/gettext/user.pot
 source_lang = en
 type        = PO
 
 [o:savoirfairelinux:p:jami:r:docs-build]
 file_filter = locales/<lang>/LC_MESSAGES/build.po
-source_file = _build/gettext/build.pot
+source_file = _build/out/gettext/build.pot
 source_lang = en
 type        = PO
 
 [o:savoirfairelinux:p:jami:r:docs-developer]
 file_filter = locales/<lang>/LC_MESSAGES/developer.po
-source_file = _build/gettext/developer.pot
+source_file = _build/out/gettext/developer.pot
 source_lang = en
 type        = PO
 
 [o:savoirfairelinux:p:jami:r:docs-index]
 file_filter = locales/<lang>/LC_MESSAGES/index.po
-source_file = _build/gettext/index.pot
+source_file = _build/out/gettext/index.pot
 source_lang = en
 type        = PO
 
 [o:savoirfairelinux:p:jami:r:docs-contribute]
 file_filter = locales/<lang>/LC_MESSAGES/contribute.po
-source_file = _build/gettext/contribute.pot
+source_file = _build/out/gettext/contribute.pot
 source_lang = en
 type        = PO
 
 [o:savoirfairelinux:p:jami:r:docs-sphinx]
 file_filter = locales/<lang>/LC_MESSAGES/sphinx.po
-source_file = _build/gettext/sphinx.pot
+source_file = _build/out/gettext/sphinx.pot
 source_lang = en
 type        = PO

Makefile

@@ -11,7 +11,7 @@ AUTOBUILD_CMD ?= sphinx-autobuild
 INTL_CMD ?= sphinx-intl
 OPTS ?=
 SRC  = .
-OUT  = _build
+OUT  = _build/out
 RSYNC_DEST ?= $(OUT)/docs
 RSYNC_OPTS ?= --verbose --archive --recursive --delete