doc: reworked install doc

    * Encourage packaged use
    * Tell more about the architecture
doc: adding a preface

Rewrite some parts of The Munin Guide.

The inspiration is *clearly* PostgreSQL's Book.
doc: fixed typo in preface
doc: build_ can be a symbolic link
doc: adding some preface

   * history
   * about
   * convention
   * bug report
doc: adding bug report section
doc: adding "getting help" section
doc: remove non-working search macro
doc: change settings
doc: fix typo in header
doc: adding "Where to Report" section
/node.d/tomcat_threads.in: Fix if {'currentThreadsBusy'} go false when it is 0, and add a total value as 'currentThreadCount' so that the chart looks more readable.
Add a lower limit of 0 to postgres database size

This ensures that the graph always starts at 0 in stead of somewhere near the
smallest database size. This makes sure that database sizes are shown
proportionally correct.
Make the postgres_size_ y-axis behaviour configurable.
ignore 'INDIVIDUAL BUFFER POOL INFO' section in MySQL 5.5

If you set innodb_buffer_pool_instances to a value greater than 1 the status
will show a new section with details about each buffer pool instance.
I think the details a currently not needed so just ignore the section.
fix parsing file io for MySQL 5.5

In MySQL 5.5 the innodb status shows additionally aio reads and aio writes for
each thread in square brackets.
fix parsing insert_buffer_and_adaptive_hash_index for MySQL 5.5

Closes munin trac ticket #1355.
fix Use of uninitialized value in printf

This fixes the case you have activated mysql_replication plugin but don't have
replication enabled in MySQL.
Without this you see the following error messages:
Use of uninitialized value in printf at /etc/munin/plugins/mysql_replication line 885
MRG: from https://github.com/cloos/munin.git branch: mysql-5.5-compatibility
Break mysql innodb data on full sections

Patch from Jan Mara
https://github.com/jmara/ubuntu-munin-mysql/commit/77ae2b2d8bc1233e0f0b0e6346d66b955441ba14