Cleanup and generalize functions of Hermitian matrices

[araujoms]

This mostly removes duplicated code. The only intentional change is to allow matrix functions to apply to any Hermitian matrix, as opposed to only Hermitian{<:Complex}. This allows them to work for matrices of quaternions, for example.

[codecov]

Codecov Report

Attention: Patch coverage is 95.23810% with 2 lines in your changes missing coverage. Please review.

Project coverage is 93.76%. Comparing base (7f354f4) to head (098966a).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/symmetric.jl	95.23%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1340      +/-   ##
==========================================
+ Coverage   93.75%   93.76%   +0.01%     
==========================================
  Files          34       34              
  Lines       15778    15743      -35     
==========================================
- Hits        14792    14762      -30     
+ Misses        986      981       -5     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[ViralBShah]

@araujoms Can I invite you to have commit access to the repo (if you don't already have it)?

[araujoms]

Sure, that would be nice, thanks! (no, I don't have it)