build(ant): change default build.dir to `.build`

.gitignore

+.build/
 build/
 test/
 local.build.properties

README.md

@@ -70,7 +70,7 @@ immediately.
 ./build_xar
 ```
 
-Artifacts will be stored in `build/`.
+Artifacts will be stored in `.build/`.
 
 The default artifact is the xar package.
 

build.xml

@@ -13,7 +13,7 @@
   <property name="project.title" value="Scalable Architecture for Digital Editions powered by TextGrid" />
   <property name="project.processorversion" value="5.2.0" />
 
-  <property name="build.dir" value="build"/>
+  <property name="build.dir" value=".build"/>
   <property name="test.dir" value="test"/>
   <property name="exist.root" value="${test.dir}/exist-distribution-${project.processorversion}"/>
   <property name="destfile" value="${build.dir}/${project.abbrev}-${project.version}.xar" />