Feature request: loop scope

Nobody has claimed this yet.

Introducing a new `loop` scope could be useful in some rules. For example:

```

rule:
meta:
name: enumerate PE sections
namespace: load-code/pe
author: "@Ana06"
scope: function
references:
- https://0x00sec.org/t/reflective-dll-injection/3080
- https://www.ired.team/offensive-security/code-injection-process-injection/reflective-dll-injection
examples:
- E4C33AC3638EEF68311F8AC0D72483C7:0x401510
features:
- and:
- offset: 0x6 = IMAGE_NT_HEADERS.FileHeader.NumberOfSections
- basic block:
- or:
- and:
- description: IMAGE_FIRST_SECTION(nt_header)
- offset: 0x14 = IMAGE_NT_HEADERS.FileHeader.SizeOfOptionalHeader
- offset: 0x18 = FileHeader.SizeOfOptionalHeader
- and:
- description: (DWORD)dll_raw + dos_header->e_lfanew + sizeof(IMAGE_NT_HEADERS) + sizeof(IMAGE_SECTION_HEADER) * i
- number: 0x28 = sizeof(IMAGE_SECTION_HEADER)
- or:
- offset/x32: 0xF8 = sizeof(IMAGE_NT_HEADERS32)
- offset/x64: 0x108 = sizeof(IMAGE_NT_HEADERS64)
- loop:
- and:
- offset: 0xC = IMAGE_SECTION_HEADER.VirtualAddress
- offset: 0x14 = IMAGE_SECTION_HEADER.PointerToRawData
- offset: 0x10 = IMAGE_SECTION_HEADER.SizeOfRawData
```

From https://github.com/fireeye/capa-rules/pull/308#discussion_r600715392

Start by reviewing the proposed rule example and the referenced capa-rules pull request discussion. No implementation files or tests are named in the issue; done would mean defining and supporting a new loop scope for rules like the PE-section example.

Written by the indexing model from the issue text.