Pullreq on MALW_Httpsd_ELF.yar, MALW_Mirai_Okiru_ELF.yar and MALW_Mirai_Satori_ELF.yar

Update Email_generic_phishing

Add rule to detect Agent Tesla information stealer malware

Create TOOLKIT_powerstager.yar

Create CVE-2017-11882.yar

Update MALW_AZORULT.yar

update rule

https://github.com/Yara-Rules/rules/issues/280

<class 'yara.SyntaxError'>: unreferenced string "$

Create APT_RemSec

Update Maldoc_PDF.yar

Change weight = 0 to 1 since 0 is not a valid weight for rule file. 
"Reason(3): Invalid weight for rule file."

indicators for remsec from Symantec white paper

Create MALW_XHide.yar

Added Maldoc_CVE_2017_11882.yar