[doc] Fix broken internal links

* Links to pages need to be relative...
* Fixes #1906

docs/pages/pmd/rules/java/design.md

@@ -1245,7 +1245,7 @@ public class Foo extends Bar {
 This rule uses the NCSS (Non-Commenting Source Statements) metric to determine the number of lines
 of code in a class, method or constructor. NCSS ignores comments, blank lines, and only counts actual
 statements. For more details on the calculation, see the documentation of
-the [NCSS metric](/pmd_java_metrics_index.html#non-commenting-source-statements-ncss).
+the [NCSS metric](pmd_java_metrics_index.html#non-commenting-source-statements-ncss).
 
 **This rule is defined by the following Java class:** [net.sourceforge.pmd.lang.java.rule.design.NcssCountRule](https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/design/NcssCountRule.java)
 
@@ -1426,7 +1426,7 @@ The NPath complexity of a method is the number of acyclic execution paths throug
 While cyclomatic complexity counts the number of decision points in a method, NPath counts the number of
 full paths from the beginning to the end of the block of the method. That metric grows exponentially, as
 it multiplies the complexity of statements in the same block. For more details on the calculation, see the
-documentation of the [NPath metric](/pmd_java_metrics_index.html#npath-complexity-npath).
+documentation of the [NPath metric](pmd_java_metrics_index.html#npath-complexity-npath).
 
 A threshold of 200 is generally considered the point where measures should be taken to reduce
 complexity and increase readability.

docs/pages/pmd/userdocs/cli_reference.md

@@ -181,7 +181,7 @@ This behavior has been introduced to ease PMD integration into scripts or hooks,
 *   [plsql](pmd_rules_plsql.html)
 *   [vf](pmd_rules_vf.html) (Salesforce VisualForce)
 *   [vm](pmd_rules_vm.html) (Apache Velocity)
-*   [xml and xsl](/pmd_rules_xml.html)
+*   [xml and xsl](pmd_rules_xml.html)
 
 
 ## Available Report Formats

docs/pages/pmd/userdocs/cpd.md

@@ -17,7 +17,7 @@ It can also be run with Maven by using the `cpd-check` goal on the [Maven PMD Pl
 
 
 Your own language is missing?
-See how to add it [here](/pmd_devdocs_major_adding_new_cpd_language.html).
+See how to add it [here](pmd_devdocs_major_adding_new_cpd_language.html).
 
 
 ### Why should you care about duplicates?

docs/pages/pmd/userdocs/installation.md

@@ -22,7 +22,7 @@ sidebar: pmd_sidebar
 
 ### Installation
 
-PMD is distributed as a zip archive, which includes both [PMD](#running-pmd-via-command-line) and [CPD](/pmd_userdocs_cpd.html). 
+PMD is distributed as a zip archive, which includes both [PMD](#running-pmd-via-command-line) and [CPD](pmd_userdocs_cpd.html). 
 You can download the latest binary distribution from [the github releases page](https://github.com/pmd/pmd/releases).
 
 Unzip it into any directory, optionally add the `bin` subdirectory in your `PATH`, and you're good to go!         

pmd-java/src/main/resources/category/java/design.xml

@@ -995,7 +995,7 @@ public class Foo extends Bar {
 This rule uses the NCSS (Non-Commenting Source Statements) metric to determine the number of lines
 of code in a class, method or constructor. NCSS ignores comments, blank lines, and only counts actual
 statements. For more details on the calculation, see the documentation of
-the [NCSS metric](/pmd_java_metrics_index.html#non-commenting-source-statements-ncss).
+the [NCSS metric](pmd_java_metrics_index.html#non-commenting-source-statements-ncss).
         </description>
         <priority>3</priority>
         <example>
@@ -1106,7 +1106,7 @@ The NPath complexity of a method is the number of acyclic execution paths throug
 While cyclomatic complexity counts the number of decision points in a method, NPath counts the number of
 full paths from the beginning to the end of the block of the method. That metric grows exponentially, as
 it multiplies the complexity of statements in the same block. For more details on the calculation, see the
-documentation of the [NPath metric](/pmd_java_metrics_index.html#npath-complexity-npath).
+documentation of the [NPath metric](pmd_java_metrics_index.html#npath-complexity-npath).
 
 A threshold of 200 is generally considered the point where measures should be taken to reduce
 complexity and increase readability.