Minor correction of xml structure to conform to the DTD
Corrections so that the documentation confirms to the DTD
[snmp/agent] Improved loading and unload of MIBs

Improved the documentation of the loading and unloading
of MIBs (plural). also added functions for loading and
unloading a single mib.

OTP-11216
[snmp/agent] Fixed doc broken link to gen_server
Fix broken spawn_opt

The option was morphed into a boolean() and then ignored.
+e should be passed through erlexec
Fix Failed-AVP construction for CEA/DWA/DPA

Send of Failed-AVP resulted in encode failure.
Correct documentation of predefined and built-in types

iodata/0, arity/0, and nonempty_list/0,1 have been added;
nonempty_maybe_improper_list/1 and maybe_improper_list/1 removed.
Convert some notes.xml files from latin-1 to utf-8

In the master branch, the encoding for most xml files have been
changed from latin-1 to utf-8. The problem is, that the corresponding
files in the maint branch still are encoded in latin-1, and that
a merge from maint to master may bring in characters encoded in latin-1
into a notes.xml file declared to be in utf-8.

To fix the problem once and for all (for the files involved), we'll
need to re-encode the files files utf-8 in maint, and then merge to
master.

Noticed-by: Magnus Henoch
Change encoding of troublesome notes.xml files to utf-8

Most notes.xml files will be updated in every release and cause
the kind of the problems described in the previous commit.
Merge branch 'bmk/snmp/agent/improve_load_unload_mibs_if/OTP-11216' into maint
Merge branch 'maint'
Merge branch 'anders/diameter/failed_avp/OTP-11293' into maint

* anders/diameter/failed_avp/OTP-11293:
  Fix Failed-AVP construction for CEA/DWA/DPA
Merge branch 'anders/diameter/spawn_opt/OTP-11299' into maint

* anders/diameter/spawn_opt/OTP-11299:
  Fix broken spawn_opt
Merge branch 'maint'
Merge branch 'kenneth/doc_to_dtd/OTP-11193' into maint

* kenneth/doc_to_dtd/OTP-11193:
  Corrections so that the documentation confirms to the DTD
  Minor correction of xml structure to conform to the DTD
Merge branch 'maint'
Merge branch 'lukas/erts/erl_exec_e' into maint

* lukas/erts/erl_exec_e:
  +e should be passed through erlexec
Merge branch 'maint'
Merge branch 'bjorn/xml-encoding-fix/OTP-11310' into maint

* bjorn/xml-encoding-fix/OTP-11310:
  Change encoding of troublesome notes.xml files to utf-8
  Convert some notes.xml files from latin-1 to utf-8