Improved configuration validation

• Unnecessary escapes are no longer permitted (e.g. ')
• Dashes are no longer permitted in identifier names (as their semantics are ambiguous)
• Unused values are detected (e.g. { "-M" })
• Validation for time ranges has been improved
• Additional validation rules for some object types (Notification and User)

New language features

• Implement a separate type for boolean values
• Support for user-defined functions
• Support for conditional statements (if/else)
• Support for 'for' and 'while' loops
• Support for local variables using the 'var' keyword
• New operators: % (modulo), ^ (xor), - (unary minus) and + (unary plus)
• Implemented prototype-based methods for most built-in types (e.g. [ 3, 2 ].sort())
• Explicit access to local and global variables using the 'locals' and 'globals' keywords
• Changed the order in which filters are evaluated for apply rules with 'for'
• Make type objects accessible as global variables
• Support for using functions in custom attributes
• Access objects and their runtime attributes in functions (e.g. get_host(NodeName).state)

ITL improvements

• Additional check commands were added to the ITL
• Additional arguments for existing check commands

CLI improvements

• Add the 'icinga2 console' CLI command which can be used to test expressions
• Add the 'icinga2 troubleshoot' CLI command for collecting troubleshooting information
• Performance improvements for the 'icinga2 node update-config' CLI command
• Implement argument auto-completion for short options (e.g. daemon -c)
• 'node setup' and 'node wizard' create backups for existing certificate files

Add ignore_soft_states option for Dependency object configuration

Fewer threads are used for socket I/O

Flapping detection for hosts and services is disabled by default

Added support for OpenTSDB

New Livestatus tables: hostsbygroup, servicesbygroup, servicesbyhostgroup

Include GDB backtrace in crash reports

Various documentation improvements

Solved a number of issues where cluster instances would not reconnect after intermittent connection problems

A lot of other, minor changes

DB IDO schema upgrade to 1.13.0 required!