Replace master document by main document (PR #41)

modules/directives/pages/include-multiple-times-in-same-document.adoc

@@ -6,7 +6,7 @@
 
 A document can include the same file any number of times.
 The problem comes if there are IDs in the included file; the output document (HTML or DocBook) will then have duplicate IDs which will make it not well-formed.
-To fix this, you can reference a dynamic variable from the main document in the ID.
+To fix this, you can reference a dynamic variable from the primary document in the ID.
 
 For example, let's say you want to include the same subsection describing a bike chain in both the operation and maintenance chapters:
 

modules/directives/pages/include-with-leveloffset.adoc

@@ -21,7 +21,7 @@ This practice is recommended whenever including AsciiDoc content to avoid unexpe
 == Manipulate heading levels with leveloffset
 
 The `leveloffset` attribute can help here by pushing all headings in the included document down by the specified number of levels.
-This allows you to publish each chapter as a standalone document (complete with a document title), but still be able to include the chapters into a master document (which has its own document title).
+This allows you to publish each chapter as a standalone document (complete with a document title), but still be able to include the chapters into a primary document (which has its own document title).
 
 You can easily assemble your book so that the chapter document titles become level 1 headings using:
 

modules/directives/pages/include.adoc

@@ -74,8 +74,8 @@ The path used in an include directive can be relative or absolute.
 
 If the path is relative, the processor resolves the path using the following rules:
 
-* If the include directive is used in the main (top-level) document, relative paths are resolved relative to the base directory.
-(The base directory defaults to the directory of the main document and can be overridden from the CLI or API).
+* If the include directive is used in the primary (top-level) document, relative paths are resolved relative to the base directory.
+(The base directory defaults to the directory of the primary document and can be overridden from the CLI or API).
 * If the include directive is used in a file that has itself been included, the path is resolved relative to the including (i.e., current) file.
 
 //TODO show examples to contrast a relative vs an absolute include
@@ -128,7 +128,7 @@ If the file is recognized as an AsciiDoc file (i.e., it has one of the following
 * preprocessor conditionals (e.g., `ifdef`)
 //* front matter (if enabled)
 
-This allows includes to be nested, and provides lot of flexibility in constructing radically different documents with a single master document and a few command line attributes.
+This allows includes to be nested, and provides lot of flexibility in constructing radically different documents with a single primary document and a few command line attributes.
 
 Including non-AsciiDoc files is normally done to merge output from other programs or populate table data: