Split out enum trait generation

[EricRahm]

This change makes the generation of EnumTraits configurable. With this change we can see reductions in code size by over 1MB. Example file size changes:

File	src (KB)	.h (KB) before	.h (KB) after
hci_events.emb	76	5356	3884
hci_commands.emb	108	5612	4268
hci_vendor.emb	32	1748	1304
hci_common.emb	32	644	368
hci_data.emb	4	152	104
l2cap_frames.emb	4	48	40
hci_h4.emb	4	8	4

This is also helpful for embedded users who couldn't use emboss due to dependencies on string libraries and functions like sscanf.

This change is split out into a series of patches to make it easier to review:

• Add forward declarations for text helpers - Cleanup in preparation for the following changes. This allows us to remove the dependency on emboss_text_util.h from the core runtime files.
• Split out enum trait generation - This is the main change, it adds a configuration flag that controls whether or not enum trait and various text helpers are generated
• Add --no-cc-enum-traits param adds a CLI flag for toggling the internal configuration
• Add bazel support for disabling enum traits adds an attribute to the emboss_cc_library to control the enum traits configuration as well as tests to make sure it works

This is part of #128

Tests: bazel test //...

[EricRahm]

Note: this builds on top of PR #133, the relevant changes start at the Add forward declarations for text helpers patch. FYI @robrussell