Release v0.7.0.dev6

|new| working SPORES mode, upgraded from v0.6 to include a selection of scoring algorithms (#716).

|new| backend set_objective method, to switch between pre-defined objectives (#716).

|changed| |backwards-incompatible| from and to parameters (to define start and end point of a transmission link) are now link_from and link_to (#717).

|changed| |backwards-incompatible| operate and spores mode configuration options are now nested within the main configuration (e.g., build.operate_window is now build.operate.window and solve.spores_number is now solve.spores.number) (#704).

|changed| coin-or-cbc is now available cross-platform on conda-forge and so is the recommended open-source solver to install a user environment with (#744).

|changed| Upper bound pins for dependencies removed where possible, to minimise clashes when using calliope as a dependency in a project (#744).

|changed| |backwards-incompatible| to ensure the model configuration always remains in sync with the results, kwargs in model.build() and model.solve() now directly affect model.config (#704)

|changed| template: can now be used anywhere within YAML definition files, not just in the nodes, techs and data_tables sections (#719).

|changed| Removed inheritance math helper function since we use base_tech for abstract base technologies and templates are now applied too early to be available later (#719).
To refer to template inheritance, set a parameter within a template as all children will share the same value.