Agent cfg with environment variables

New Feature enables Jacoco agent to output "exec" results to a platform dependent directory. Examples <code>java.io.tempdir</code> or <code>user.home</code>. 

Example setting the agent's <code>destfile</code> in <code>jacoco-agent.properties</code>:

<pre>replaceproperties=true
destfile=${user.home}/coverage-data/coverage.exec
</pre>

The replacement feature is disabled by default. It can be enabled by 
adding <code>replaceproperties=true</code> in agent's 
<code>jacoco-agent.properties</code>. Alternatively the file's
configuration can be overridden by the system property
<code>-Djacoco-agent.replaceproperties=true</code> on java command
line.

The initial escaping mechanism was removed due to conflicts with Windows paths and anonymous classes (for more details see documentation). Documentation has been updated and explains the effects of enabling <code>replaceproperties</code>.