Shorten the document titles

The page titles were restating the project name and the artifact names
they cover. They read as Overview, DPM Design, Interaction with
libdpm-core.so, and Building DPM Core and CLI.

docs/BUILD.md

@@ -1,4 +1,4 @@
-# Building libdpm-core.so and the dpm Binary {#build}
+# Building DPM Core and CLI {#build}
 
 ## Prerequisites
 

docs/CONSUMERS.md

@@ -1,4 +1,4 @@
-# Consuming libdpm-core.so {#consumers}
+# Interaction with libdpm-core.so {#consumers}
 
 Programs link libdpm-core.so as an ordinary shared library dependency — the same way they link any other library — to reach the package manager in-process: build systems, installers, image builders, system tooling, and foreign-language bindings all use the library the `dpm` binary is built on. A program holding a default context is working against system configuration, the system module path, the system tree, and system locking, the same environment the installed `dpm` binary sees.
 

docs/DESIGN.md

@@ -1,4 +1,4 @@
-# DPM — Dark Horse Package Manager: Design {#design}
+# DPM Design {#design}
 
 ## Constraints
 

docs/OVERVIEW.md

@@ -1,4 +1,4 @@
-# DPM — An Overview {#overview}
+# Overview {#overview}
 
 ## What DPM Is